Category Archives: Networking

Debian on WD EX2100

The Western Digital My Cloud EX2100 is a dual-bay NAS based on the Marvell Armada 385 dual core ARMv7 CPU first released in 2015.

In terms of NAS devices available in 2017, it isn’t very special. I would say the only major differences between most other devices in the 2 bay category are:

  • Dual Gigabit Ethernet
  • Screwless and trayless hard drive installation

The dual GigE interfaces are what attracted me to the device over competitors like the Zyxel NAS326 and Western Digital’s own MyCloud EX2 Ultra.

Unlike some other NAS bundles, it’s possible to buy the EX2100 without drives, so you can add your own preferred 3.5″ SATA hard drives. I bought a refurbished unit for 110€, which seems typical for a device with these features. For some reason the resale price of these units has skyrocketed since I bought mine in mid-2017. I personally would not pay more than 150€ for such a device. If you get into the higher price range of these SOHO devices, you’re almost always going to get better value for your money building your own NAS using standard x86 components (such as the HP MicroServer G7/Gen 8/Gen 10) and a distribution like FreeNAS or OpenMediaVault.

Since the vendor supplied firmware is almost always a pile of unsightly hacks, I set to work investigating into how to put a better operating system on the EX2100. If you stick around to the end, you’ll see this particular product also has its share of unfortunate hardware design decisions…

kwboot
Before we get into anything about u-boot or the operating system, we need to talk about kwboot.

kwboot stands for “Kirkwood boot”

Kirkwood is an ARMv5 SoC from Marvell around 2008-2009 that started out in the SheevaPlug (what single board computers were before the creation of the Raspberry Pi) and sooner or later found its way into a lot of NAS devices like the D-Link DNS320 and the Zyxel NSA320.

Coming back to the near-past (2015), and we have the Western Digital EX2100/4100 which use the Marvell Armada 385/388 CPU, which is a dual-core ARMv7 design. However it was known that the Armada SoC could boot from serial because of the SolidRun ClearFog. But the ClearFog uses DIP switches to set the boot source, and most (all?) consumer devices lack these.

ClearFog Pro boot source selection DIP switches

It turns out it is possible to kwboot consumer devices based on the Armada 38x, however you need to apply this patch to kwboot to parse the response from the Armada CPU, which differs from the Kirkwood response. Unfortunately the patch broke Kirkwood compatibility, and was seemingly never merged into u-boot mainline. However, you can still apply it to the kwboot source in u-boot and compile kwboot for use with Armada CPUs.

Once you have patched kwboot, you can use it to test new versions of u-boot via a USB to uart adapter:
$ ./kwboot -f -t -B 115200 /dev/ttyUSB0 -b u-boot-uart.bin -s 0 -q 1

There are some synchronization issues with the magic sequence, so it often takes several attempts before successfully loading via kwboot. A dead giveaway that you need to power cycle the device and try again is when you immediately see u-boot output in the console instead of “Sending boot image…”

A successful attempt should look similar to the following:
$ ./kwboot -f -t -B 115200 /dev/ttyUSB0 -b u-boot-a38x-Yosemite_2014T3_PQ-nand-uart.bin -s 0 -q 1
Sending boot message. Please reboot the target...-�$�"Ufw�$�"U����$
Dfw�$�"U�\�$�"U����$�DUf�$�"Uw��"U����$4"U���$�"Uw�$�"U���$�DUf|fD�&T���$�"U�E�$�"Df3DD�DU�E7$�"U����$4"U���$�"U�E�4"U�/[email protected]� ��$DUw�$�"U����$�DUff�$�"D��fD$U��
Sending boot image...
0 % [......................................................................]

Once kwboot works, you can safely proceed to testing u-boot modifications without the risk that you brick your device, as kwboot runs code in memory without modifying the contents of NAND.

u-boot
Unfortunately mainline u-boot doesn’t support this device, although similar devices are supported, such as the Turris Omnia (Armada 385) and Solidrun Clearfog Pro (Armada 388). It’s no surprise that attempting to kwboot a build of mainline u-boot for these targets on the EX2100 doesn’t work. So currently we have no choice but to use the u-boot source from Western Digital’s GPL archive.

The stock u-boot on the device does not support saveenv. Without modifying NAND, it is possible to boot Linux from USB, however this requires using the uart console and manually entering the boot parameters on each boot.

Naively modifying the WD u-boot source to enable the saveenv command results in corruption of the kernel uImage since someone at WD set the environment offset to 5MB and this is beyond the u-boot partition, corrupting the uImage.

However it is possible to modify the WD u-boot source to save environment variables within the 5MB allocated for u-boot. This requires reflashing u-boot to the device. Before you replace the stock u-boot on your device, you should take a backup of the u-boot region of flash. This can be done from within the Western Digital firmware, but requires a USB to UART adapter and a header soldered to the PCB:
# nanddump --noecc --omitoob -f mtd0.bin /dev/mtd0

Remember to copy this file somewhere off-device, such as a USB key, for safe keeping!

The general steps to replace the stock u-boot are:

  1. kwboot a modified u-boot which saves environment variables within u-boot region
  2. Inside u-boot, run saveenv
  3. Boot Debian from USB or SATA
  4. Dump u-boot env to a file (using nandread)
  5. Erase u-boot portion of mtd0 (using flash_erase)
  6. Flash new u-boot (using nandwrite)
  7. Restore u-boot environment variables (using nandwrite)
  8. Reboot

Dump the u-boot env to a file:
# nanddump -s 0x100000 -l 0x80000 -f ubootenv.bin /dev/mtd0

Erase the u-boot portion of mtd0 and flash the new u-boot to NAND:
# flash_erase /dev/mtd0 0 8
# nandwrite -p /dev/mtd0 u-boot-a38x-Yosemite_2014T3_PQ-nand.bin

Restore u-boot environment variables:
# nandwrite -p /dev/mtd0 -s 0x100000 ubootenv.bin

Integrated MCU
Western Digital decided to use an external microcontroller to handle certain system management functions such as fan control, LED control, and power on/off.

Sadly the microcontroller uses a proprietary and undocumented protocol for communication, and as it turns out this protocol can differ even between Western Digital products!

For the Western Digital EX2100 and EX4100, the integrated microcontroller communicates on ttyS1 at 115200n8, unlike other Western Digital NAS products whose microcontroller communicates at 19200n8.

Thankfully, some of the commands are common, so once communication with the microcontroller has been established, fan control and temperature monitoring are functional. Fan control and temperature monitoring are available through a userspace daemon called “mcm-daemon” (MyCloud Mirror daemon). I have forked the mcm-daemon repository on GitHub and made modifications to support the EX2100/4100.

LED control and power on/off are still a work in progress as the reverse engineered commands used on other WD products do not work on the EX2100/4100.

Debian
The user bodhi at Doozan forums does a great job of providing pre-built Debian images for a variety of Marvell Armada based NAS devices.

Usually I would link to the excellent instructions bodhi normally writes for installing Debian, but since they don’t have the EX2100, writing the instructions fell to me.

But sadly I haven’t got installation instructions written because I’ve bricked my EX2100.

Weltrend WT61P8
Let’s revisit this mystery microcontroller in charge of so many tasks in the EX2100.

Well, after reading that Western Digital My Cloud products contained a backdoor and multiple vulnerabilities I thought I would go and update the WD firmware before continuing to write the Debian installation instructions. The WD firmware resides on the built in 512MB of EMMC, while Debian lives on a USB device, so the installation of Debian does not replace the original WD firmware.

During the WD update process I noticed that it was also updating the firmware of the Weltrend:

16479 root 6624 S /var/www/cgi-bin/system_mgr.cgi
16480 root 2560 S sh -c cd /usr/local/upload/;upload_firmware -a -n 'nas-new-firmware' >/dev/null;cd /
16481 root 4544 S upload_firmware -a -n nas-new-firmware
19436 root 49120 R mcu_upgrade -r -f /tmp/uP_0.bin
19552 root 2720 R ps ax

How curious! Since the Weltrend is very undocumented I was eager to learn more about the firmware it runs.

I found out a good deal more than I’d expected. Firstly, the mcu_upgrade binary contains some interesting strings. Here is a short sample of strings in the binary:

WT61P8
Enable ISP
Set ISP
Erase
Page Erase
Program
Set Address High Byte
Finish

The MCU firmware also has some very interesting strings. Here is a short sample of strings in the firmware:

nick 1111
nick 2222
nick 3333
nick 4444
MyCloudDL2000
Cannot Copy
from Camera
Cannot Move
Storage
Almost Full
Limit Reached
nick pwr on
nick pwr off 1
nick pwr off wol
Welcome to
RTC_ALARM pwr on

Googling the part number “WT61P8” lead to a very interesting datasheet (PDF) describing the microcontroller in detail.

What I found from the datasheet was… not anything I expected to find.

It’s a Turbo 8052 CPU with ~48KB of built-in EEPROM (this is my guess based on the part number and size of firmware mcu_upgrade was sending) and it’s a “Flat Panel Display Control Sub-MCU”

Most information about Weltrend microcontrollers is on Russian language forums dedicated to TV repair. The most common use of this MCU is in Samsung TVs for power management, since it includes an IR receiver and HDMI CEC capabilities.

They do support ISP (In-system Programming) via I2C, if you have the right hardware. There are quite a few Russian articles and YouTube videos on how to program these chips in TVs.

Conclusion

After reading about WD’s numerous firmware vulnerabilities and a back door, which were also present in D-Link NAS products (implying a shared code base or same third party contractor), and then learning that the microcontroller in charge of power management for the EX2100 (and other My Cloud products) was intended for power management in LCD TVs:

My final $0.02: this thing is an utter bodge job in both hardware and software! Don’t buy one of these. It doesn’t matter that can be persuaded to run Debian, it’s terrible value for the price.

You’re far better off getting an older PC and running FreeNAS or OpenMediaVault. Older corporate tower PCs with 2nd or 3rd gen Intel processors like the Dell Optiplex line can easily be purchased for under $150 from places like eBay.

If power consumption is really important to you, then I would recommend something like the Rock64 which has Gigabit Ethernet and excellent USB 3.0 performance with Armbian. It also comes with more RAM than the EX2100 (1/2/4GB while EX2100 has only 1GB) and is a quad core aarch64 instead of dual core armv7!

Best of all, an older PC or Pine64 is going to be cheaper than the EX2100 (or ludicrously more expensive 4 bay EX4100) anyway.

If I ever manage to restore the Weltrend firmware rest assured there will be a follow up article with both the journey of unbricking and instructions to install Debian. Until then, I’m going to take the HDDs I planned to use in the EX2100 and build a FreeNAS in an old PC. ✌️

Allwinner H2+/H3 Ethernet with Linux 4.9-rc8

The Orange Pi PC is not a new single board computer. It’s been released for over a year now, but has mostly been stuck on a heavily patched 3.4 release kernel.

There have been ongoing efforts since the release to have support for the Allwinner H3 in the mainline kernel. In the past weeks there have been new patches released which enable support for the Ethernet MAC on the H3 (and H2+).

Unfortunately this support is not in mainline yet, and won’t make it in the upcoming 4.9 release. However, that doesn’t stop you from taking the patches and applying them against 4.9 yourself.

I wrote a script to compile the kernel from source, applying the necessary patches to the kernel and using a minimal .config file which compiles the sun8i_emac support as a module. You can download the build script from GitHub.

It does try to be somewhat smart: verifying the integrity of the downloaded files, and will bail out if there are errors in patching the source code. But, it doesn’t do toolchain dependency checking because that’s just too complicated. Since the emac support will end up in mainline soon, I doubt it’s worth the time to improve the build script. However if anyone is interested in improving it, the script is released as GPLv2.

The result? If you are patient enough to wait for the kernel to compile, you get a uImage and modules for Linux 4.9-rc8 with Ethernet support:

Allwinner H3 emac performance:

[email protected]:~$ iperf -n 1024M -c 192.168.1.150
————————————————————
Client connecting to 192.168.1.150, TCP port 5001
TCP window size: 43.8 KByte (default)
————————————————————
[ 3] local 192.168.1.206 port 42572 connected with 192.168.1.150 port 5001
[ ID] Interval Transfer Bandwidth
[ 3] 0.0-100.6 sec 1.00 GBytes 85.4 Mbits/sec

Orange Pi Zero (Allwinner H2+):

I’ve also just received my Orange Pi Zero and confirmed that the same kernel works on the Orange Pi Zero, so you can run Linux 4.9 on the Orange Pi PC (Allwinner H3) or Orange Pi Zero (Allwinner H2+) with Ethernet support.

Allwinner H2+ emac performance:

[email protected]angePI:~$ iperf -n 1024M -c 192.168.1.150
————————————————————
Client connecting to 192.168.1.150, TCP port 5001
TCP window size: 43.8 KByte (default)
————————————————————
[ 3] local 172.16.4.206 port 54762 connected with 192.168.1.150 port 5001
[ ID] Interval Transfer Bandwidth
[ 3] 0.0-95.9 sec 1.00 GBytes 89.5 Mbits/sec

Download:
If you want to skip compiling the kernel yourself, I’m providing the kernel uImage and modules here.

I am using u-boot v2016.11 from denx.

Note: HDMI isn’t working on my Orange Pi PC, and since I run it headless I’m not interested in investigating why. If you’re using your Orange Pi PC with HDMI output, you may need to modify the kernel .config file to fix HDMI.

D-Link DAP-1520 hacking: Part 2

In Part 1 we looked at the hardware of the DAP-1520 and did some investigation into the stock D-Link firmware that runs on the device.

We found that there were two firmware images on the device, the main firmware (Image 1) and the recovery OS (Image 2) which is used when Image 1 fails verification.

Despite D-Link’s reputation for buggy firmwares, my infosec skills are still basic, and I wasn’t able to get telnetd running on the DAP-1520 to investigate the firmware more. Sure, we already have a dump of the firmware thanks to an SPI reader (and the update, available from D-Link’s website), but this only tells us what’s in the firmware, it doesn’t actually let us poke around at the hardware. Since my stated goal is to get OpenWrt running on the device, poking around at the hardware with a working OS is pretty important.

To accomplish this, I needed to build the firmware from the GPL source code published by D-Link. You can download the GPL source code for their routers from their Taiwanese website.

DAP-1520 GPL source code

DAP-1520 GPL source code

GPL source code for each firmware release

GPL source code for each firmware release

If you’re wondering why there’s a huge difference in the size of the source code between firmware versions, don’t. Firmware 1.05, despite the file extension, is just a tar file and is 185MB. Firmware 1.06 is a gzip compressed tar file and is 186MB. These inconsistencies are just the start of our wonderful journey with the D-Link source 😉

I’m building firmware 1.06, since newer is always better. I’ve just noticed that D-Link have published a file for firmware 1.07 on their Australian website. Hopefully they will release the GPL source for this firmware soon, I’m excited to see what vulnerabilities have been addressed in the web configurator!

Anyway, when you download the GPL source code, you will find that D-Link has included a README file, which describes how to build the firmware. This surprised me, I wasn’t expecting anything more than the source code, so some minor kudos go to D-Link for at least providing instructions.

Install & Build
===============
Environment: 
    1. Download Ubuntu 10.04.4 LTS from http://releases.ubuntu.com/lucid/
        http://releases.ubuntu.com/lucid/ubuntu-10.04.4-server-i386.iso
    2. Install Ubuntu 10.04.4 LTS server in your computer.
    3. Make sure your Ubuntu is 10.04.4 LTS(Lucid Lynx).
    4. Building image with ROOT privileges.	
	
Install:
    1.  Please update the list of available packages:
       ~#apt-get update
	   ~#apt-get install gcc build-essential zlib1g-dev bison flex subversion sharutils libncurses5-dev gawk help2man intltool pkg-config libglib2.0-dev	  
    2. Create a folder in root directory 
       ~#mkdir /tftpboot/
    3. Install the toolchain:
		~#cd /DAP-1520_A1_106b04_FOSS/toolchain
		A.	GCC
				1.	cp buildroot-gcc342.tar.bz2 /opt
				2.	tar jxvf buildroot-gcc342.tar.bz2
		B.	LZMA
			    1.  cp lzma-4.32.7.tar.gz /home/
			    2.  tar -xvf lzma-4.32.7.tar.gz
				3.  cd lzma-4.32.7
				4.	./configure
				5.	make
				6.	make install
			    7.  ldconfig	
		C.	XZ
				1.	cp xz-5.0.3.tar.bz2 /home/
				2.	tar jxvf xz-5.0.3.tar.bz2
				3.  cd xz-5.0.3
				4.	./configure
				5.	make
				6.	make install
		D.	mksquashfs
				1.  cp squashfs4.2.tar.bz2 /home/
				2.	tar jxvf squashfs4.2.tar.bz2
				3.	cd squashfs4.2/squashfs-tools
				4.	make
				5.	cp mksquashfs /opt/buildroot-gcc342/bin/mksquashfs_lzma-4.2
	4. Building the image & loader.
		(1). Please make sure the gcc-version is greater than 4.2.4
			 (You can type "~#gcc -v " to check the gcc-version)
		(2). Copy the DAP1520A1_GPL106b04.tar into /home/ directory
		     use following commands.
			~#tar -xvf DAP1520A1_GPL106b04.tar
		(3). You will get "AthSDK" directory.
			~#cd /home/AthSDK	
		(4). Into the AthSDK directory,and run following commands.
			(4-1). If you want to build normal image
			~#make clean
			~#make kernel_clean
			~#make 
			After make successfully, under "AthSDK/image/", you will get the normal image file "DAP1520A1_FW106B04.bin".
			(4-2). If you want to build backup image
			~#make -f Makefile.backup clean
			~#make kernel_clean
			~#make -f Makefile.backup 
			After make successfully, under "AthSDK/image/", you will get the backup image file "DAP1520A1_FW100B03.bin".
			(4-3). If you want to build loader
			~#make loader_clean
			~#make mtk_loader
			After make successfully, under "AthSDK/image/", you will get the loader file "DAP1520A1_FW100.boot".
	5. Update the new firmware by web interface provided by device.
	6. Congratulations! You got your specific image now.

Install Ubuntu 10.04? Thanks, I think I will pass. Ubuntu 10.04 isn't supported anymore, so good luck installing all the packages you need to support the build environment. So, instead I decided to build the firmware on my laptop, which runs a reasonably current version of Arch Linux. On Arch Linux /tmp is a ramdisk, so I just do all my work there and make symlinks when necessary. I wouldn't recommend using /tmp for work unless you have >8GB of RAM as the /tmp filesystem is by default 50% of your RAM, and the compiled source code is somewhere around 2GB give or take.

The first step is to decompress the toolchain and create a symlink from DAP-1520_A1_106b04_FOSS/toolchain/ to /opt/buildroot-gcc342 because a bunch of their makefiles are hard coded to look in this place for the toolchain.

$ cd $(mktemp -d)
$ tar -zxvf ~/Downloads/DAP-1520\ A1_ver1.06b04_FOSS.tar.gz
$ cd DAP-1520_A1_106b04_FOSS/toolchain
$ tar -jxf buildroot-gcc342.tar.bz2
$ tar -zxf lzma-4.32.7.tar.gz
$ tar -jxf squashfs4.2.tar.bz2
$ ln -s $(pwd)/buildroot-gcc342 /opt/buildroot-gcc342

Then you'll need to compile the versions of lzma and squashfs provided, for reasons which I will get into in a bit. Copy the lzma and mksquashfs_lzma-4.2 binaries into the bin folder of your toolchain. I don't recommend running make install as they do in the instructions, just run make and manually copy the binaries to the toolchain/bin directory.

$ cd lzma-4.32.7
$ ./configure
$ make
$ cp src/lzma/lzma ../buildroot-gcc342/bin/
$ cd ../squashfs4.2/squashfs-tools
$ make
$ cp mksquashfs ../../buildroot-gcc342/bin/mksquashfs_lzma-4.2

The copy of mksquashfs_lzma-4.2 included in the toolchain links against an ancient version of liblzma.so which has long since not existed in Arch Linux. Hence, it's easier just to compile the version from the source code included. Just install xz from your package manager, I didn't need to compile their specific version.

Now that we have "installed" the toolchain, we need to decompress the actual source code for the router firmware and "install" it in /home/AthSDK:

$ cd ../../../src/
$ tar -zxf DAP1520A1_GPL106b04.tar.gz
$ sudo ln -s $(pwd)/AthSDK /home/AthSDK

Now we are all set to start building it as per the D-Link instructions above:

$ cd AthSDK
$ make clean
$ make kernel_clean

At this point, we need to fix some of the source files or the compilation will fail. You will need to download and run the next few patches in the AthSDK directory or compilation will fail with errors.

$ wget https://watchmysys.com/blog/wp-content/uploads/2016/03/timeconst.patch
$ wget https://watchmysys.com/blog/wp-content/uploads/2016/03/busybox_makefile.patch
$ wget https://watchmysys.com/blog/wp-content/uploads/2016/03/busybox_features.patch
$ wget https://watchmysys.com/blog/wp-content/uploads/2016/03/timer_makefile.patch
$ wget https://watchmysys.com/blog/wp-content/uploads/2016/03/telnetd.patch
$ wget https://watchmysys.com/blog/wp-content/uploads/2016/03/nc.patch

Some explanation is in order:

  • Compiling the kernel will fail because Arch has a reasonably new verison of Perl, and the syntax in Perl >5.22 has changed since 2.6.36. You will need to apply the patch timeconst.patch to fix this.
  • Compiling busybox will fail because the syntax in the makefile is deprecated. You will need to apply the patch busybox_makefile.patch to fix this.
  • We want to have telnetd and nc in the image we create, for backdoors and stuff. You will need to apply the patch busybox_features.patch to enable these features.
  • D-Link includes an application called timer which expects an object file to compile, except this object file is never created. Removing the line fixes the error and as far as I know timer still works as intended. You will need to apply the patch timer_makefile.patch to fix this.
  • We need to create sysconfig scripts to start the telnetd and nc daemons on boot. The telnetd and nc patches create the sysconfig scripts in the rootfs folder of the D-Link OS
  • $ patch -p1 < timeconst.patch 
    patching file platform/MT7620/kernels/mips-linux-2.6.36.x/kernel/timeconst.pl
    $ patch -p1 < busybox_makefile.patch 
    patching file apps/busybox-1.6.1/Makefile
    $ patch -p1 < busybox_features.patch 
    patching file apps/busybox-1.6.1/.config
    $ patch -p1 < timer_makefile.patch   
    patching file apps/timer/Makefile
    $ sudo patch -p1 < telnetd.patch  
    patching file rootfs/target/etc/sysconfig/S3telnetd.sh
    $ sudo patch -p1 < nc.patch      
    patching file rootfs/target/etc/sysconfig/S4nc.sh
    $ chmod 755 rootfs/target/etc/sysconfig/*sh
    $ install -d rootfs/target/bin
    $ ln -s busybox_161 rootfs/target/bin/nc
    

    Now we can run the next command with sudo, as tar will attempt to create some files for the firmware which are owned by root. This will fail if not run as sudo:

    $ sudo make

    A long time later:

    
    =================== installing wireless ===================
    make -C wireless install || exit 1
    make[1]: Entering directory '/tmp/tmp.41xjcpqbrX/DAP-1520_A1_106b04_FOSS/src/AthSDK/wireless'
    make[1]: Leaving directory '/tmp/tmp.41xjcpqbrX/DAP-1520_A1_106b04_FOSS/src/AthSDK/wireless'
    =================== installing rootfs ===================
    make -C rootfs install || exit 1
    make[1]: Entering directory '/tmp/tmp.41xjcpqbrX/DAP-1520_A1_106b04_FOSS/src/AthSDK/rootfs'
    install -d /home/AthSDK/image
    rm -rf /home/AthSDK/rootfs/target/man/ /home/AthSDK/rootfs/target/lib/*.a
    Strip all .so
    find /home/AthSDK/rootfs/target/lib/ -name "*.so*" -exec mipsel-linux-uclibc-strip '{}' ';'
    cp -f /opt/buildroot-gcc342/lib/libdl* /home/AthSDK/rootfs/target/lib/
    mipsel-linux-uclibc-strip target/lib/libdl-0.9.30.so
    mipsel-linux-uclibc-strip: 'target/lib/libdl-0.9.30.so': No such file
    Strip all exec
    find /home/AthSDK/rootfs/target -type f -perm -u+x -exec mipsel-linux-uclibc-strip '{}' ';'
    mipsel-linux-uclibc-strip: /home/AthSDK/rootfs/target/www/widget.cgi: File format not recognized
    mipsel-linux-uclibc-strip: /home/AthSDK/rootfs/target/www/tr069.cgi: File format not recognized
    mipsel-linux-uclibc-strip: /home/AthSDK/rootfs/target/www/save_configure.cgi: File format not recognized
    mipsel-linux-uclibc-strip: /home/AthSDK/rootfs/target/www/hnap.cgi: File format not recognized
    mipsel-linux-uclibc-strip: /home/AthSDK/rootfs/target/www/apply.cgi: File format not recognized
    mipsel-linux-uclibc-strip: /home/AthSDK/rootfs/target/www/library/test/success.html: File format not recognized
    mipsel-linux-uclibc-strip: /home/AthSDK/rootfs/target/usr/share/udhcpc/default.script: File format not recognized
    mipsel-linux-uclibc-strip: /home/AthSDK/rootfs/target/usr/share/udhcpc/default.bound-nodns: File format not recognized
    mipsel-linux-uclibc-strip: /home/AthSDK/rootfs/target/usr/share/udhcpc/default.bound-dns: File format not recognized
    mipsel-linux-uclibc-strip: /home/AthSDK/rootfs/target/lib/libavahi-core.la: File format not recognized
    mipsel-linux-uclibc-strip: /home/AthSDK/rootfs/target/lib/libavahi-common.la: File format not recognized
    mipsel-linux-uclibc-strip: /home/AthSDK/rootfs/target/lib/libexpat.la: File format not recognized
    mipsel-linux-uclibc-strip: /home/AthSDK/rootfs/target/lib/libdaemon.la: File format not recognized
    mipsel-linux-uclibc-strip: /home/AthSDK/rootfs/target/etc/rdnssd-script: File format not recognized
    mipsel-linux-uclibc-strip: /home/AthSDK/rootfs/target/etc/dhcp6c-script: File format not recognized
    mipsel-linux-uclibc-strip: /home/AthSDK/rootfs/target/etc/host.conf: File format not recognized
    mipsel-linux-uclibc-strip: /home/AthSDK/rootfs/target/etc/inittab: File format not recognized
    mipsel-linux-uclibc-strip: /home/AthSDK/rootfs/target/etc/services: File format not recognized
    mipsel-linux-uclibc-strip: /home/AthSDK/rootfs/target/etc/shadow: File format not recognized
    mipsel-linux-uclibc-strip: /home/AthSDK/rootfs/target/etc/rdnssd/merge-hook: File format not recognized
    mipsel-linux-uclibc-strip: /home/AthSDK/rootfs/target/etc/passwd: File format not recognized
    mipsel-linux-uclibc-strip: /home/AthSDK/rootfs/target/etc/sysinfo: File format not recognized
    mipsel-linux-uclibc-strip: /home/AthSDK/rootfs/target/etc/icon.ico: File format not recognized
    mipsel-linux-uclibc-strip: /home/AthSDK/rootfs/target/etc/nvram.default: File format not recognized
    mipsel-linux-uclibc-strip: /home/AthSDK/rootfs/target/etc/sysconfig/S2gpio.sh: File format not recognized
    mipsel-linux-uclibc-strip: /home/AthSDK/rootfs/target/etc/issue: File format not recognized
    mipsel-linux-uclibc-strip: /home/AthSDK/rootfs/target/etc/group: File format not recognized
    mipsel-linux-uclibc-strip: /home/AthSDK/rootfs/target/etc/fstab: File format not recognized
    mipsel-linux-uclibc-strip: /home/AthSDK/rootfs/target/etc/securetty: File format not recognized
    mipsel-linux-uclibc-strip: /home/AthSDK/rootfs/target/etc/rc.d/rcS: File format not recognized
    mipsel-linux-uclibc-strip: /home/AthSDK/rootfs/target/bin/gpio_event: File format not recognized
    Strip Atheros's *.ko
    find /home/AthSDK/rootfs/target/lib/modules/2.6.36.x -name "*.ko" -type f \
    	-exec mipsel-linux-uclibc-strip -g -S -d \
    	--strip-unneeded \
    	--remove-section=__kcrctab \
    	--remove-section=__kcrctab_gpl \
    	--remove-section=__param \
    	--remove-section=__ex_table \
    	--remove-section=__obsparm \
    	--remove-section=__versions \
    	--remove-section=.pdr \
    	--remove-section=.mdebug.abi32 \
    	--remove-section=.comment \
    	--remove-section=__ksymtab_gpl_future \
    	--remove-section=__kcrctab_gpl_future \
    	--remove-section=__ksymtab_unused \
    	--remove-section=__kcrctab_unused \
    	--remove-section=__ksymtab_unused_gpl \
    	--remove-section=__kcrctab_unused_gpl \
    	--remove-section=.ctors \
    	--remove-section=__markers \
    	--remove-section=__tracepoints \
    	--remove-section=_ftrace_events \
    	--remove-section=__mcount_loc \
    	-x '{}' ';'
    Strip Cameo's *.ko
    Remove unneeded files
    rm -f /home/AthSDK/rootfs/target/lib/modules/2.6.36.x/build
    rm -f /home/AthSDK/rootfs/target/lib/modules/2.6.36.x/modules.order
    rm -f /home/AthSDK/rootfs/target/lib/modules/2.6.36.x/source
    rm -rf /home/AthSDK/rootfs/target/include
    rm -rf /home/AthSDK/rootfs/target/lib/avahi
    rm -rf /home/AthSDK/rootfs/target/lib/pkgconfig
    rm -rf /home/AthSDK/rootfs/target/root
    rm -f /home/AthSDK/rootfs/target/lib/modules/2.6.36.x/net/ath_pktlog.ko
    cp /home/AthSDK/platform/MT7620/kernels/mips-linux-2.6.36.x/arch/mips/boot/vmlinux.* /home/AthSDK/image/ || exit 1;
    /home/AthSDK/tools/release_scripts/mkuImage.sh
    + case $BOARD_TYPE in
    + LDADDR=0x80000000
    ++ readelf -a /home/AthSDK/platform/MT7620/kernels/mips-linux-2.6.36.x/vmlinux
    ++ grep Entry
    ++ head -1
    ++ cut -d: -f 2
    + ENTRY='               0x8000c310'
    + /home/AthSDK/tools/release_scripts/mkimage -A mips -O linux -T kernel -C lzma -a 0x80000000 -e 0x8000c310 -n 'Linux Kernel Image' -d /home/AthSDK/image/vmlinux.lzma /home/AthSDK/image/vmlinux.lzma.ub
    Image Name:   Linux Kernel Image
    Created:      Sun Mar  6 23:20:20 2016
    Image Type:   MIPS Linux Kernel Image (lzma compressed)
    Data Size:    908125 Bytes = 886.84 kB = 0.87 MB
    Load Address: 0x80000000
    Entry Point:  0x8000C310
    /home/AthSDK/tools/release_scripts/release_rootfs.sh
    =================== Create SQUASHFS for DAP-1520 ===================
    Parallel mksquashfs: Using 4 processors
    Creating 4.0 filesystem on /home/AthSDK/image/MT7620-squash, block size 65536.
    [===========================================================================================\] 524/524 100%
    Exportable Squashfs 4.0 filesystem, xz compressed, data block size 65536
    	compressed data, compressed metadata, compressed fragments, compressed xattrs
    	duplicates are removed
    Filesystem size 3370.39 Kbytes (3.29 Mbytes)
    	28.91% of uncompressed filesystem size (11656.43 Kbytes)
    Inode table size 5286 bytes (5.16 Kbytes)
    	24.23% of uncompressed inode table size (21816 bytes)
    Directory table size 5948 bytes (5.81 Kbytes)
    	46.62% of uncompressed directory table size (12759 bytes)
    Number of duplicate files found 46
    Number of inodes 650
    Number of files 419
    Number of fragments 56
    Number of symbolic links  125
    Number of device nodes 53
    Number of fifo nodes 0
    Number of socket nodes 0
    Number of directories 53
    Number of ids (unique uids + gids) 1
    Number of uids 1
    	root (0)
    Number of gids 1
    	root (0)
    =================== MAX_ROOTFS_IMG_SIZE=3801062 Bytes =================== 
    0+1 records in
    1+0 records out
    3801062 bytes (3.8 MB) copied, 0.00318195 s, 1.2 GB/s
    =================== MT7620 Squashfs created for 8 MB FLASH ===================
    /home/AthSDK/tools/release_scripts/release_image.sh
    0+1 records in
    1+0 records out
    983040 bytes (983 kB) copied, 0.00105716 s, 930 MB/s
    make[1]: Leaving directory '/tmp/tmp.41xjcpqbrX/DAP-1520_A1_106b04_FOSS/src/AthSDK/rootfs'
    =================== Finish ===================
    

    We need to verify that the file produced matches the official firmware update available from D-Link. It really wouldn't do to flash an XZ compressed kernel when the bootloader expects an LZMA compressed kernel!

    $ binwalk image/DAP1520A1_FW106B04.bin 
    
    DECIMAL       HEXADECIMAL     DESCRIPTION
    --------------------------------------------------------------------------------
    0             0x0             uImage header, header size: 64 bytes, header CRC: 0x9D3D95E7, created: 2016-03-07 19:18:42, image size: 909160 bytes, Data Address: 0x80000000, Entry Point: 0x8000C310, data CRC: 0x77D76472, OS: Linux, CPU: MIPS, image type: OS Kernel Image, compression type: lzma, image name: "Linux Kernel Image"
    64            0x40            LZMA compressed data, properties: 0x5D, dictionary size: 33554432 bytes, uncompressed size: 2798288 bytes
    983040        0xF0000         Squashfs filesystem, little endian, version 4.0, compression:xz, size: 3451228 bytes, 650 inodes, blocksize: 65536 bytes, created: 2016-03-07 19:18:45

    Good, this matches the D-Link provided firmware update, so we should be all good to flash it to the router and see if we can login.

    Gotchas
    mksquashfs
    I had originally installed mksquashfs from pacman, because why would you want to use the old version included in the D-Link source?

    Hilariously, the version of mksquashfs_lzma-4.2 included in the D-Link source doesn't actually support LZMA compression at all, instead using xz compression by default!

    
    SYNTAX:/opt/buildroot-gcc342/bin/mksquashfs_lzma-4.2 source1 source2 ...  dest [options] [-e list of exclude
    dirs/files]
    
    Filesystem build options:
    -comp 		select  compression
    			Compressors available:
    				gzip
    				xz (default)
    
    (other options omitted)
    
    Compressors available and compressor specific options:
    	gzip (no options)
    	xz (default)
    	  -Xbcj filter1,filter2,...,filterN
    		Compress using filter1,filter2,...,filterN in turn
    		(in addition to no filter), and choose the best compression.
    		Available filters: x86, arm, armthumb, powerpc, sparc, ia64
    	  -Xdict-size 
    		Use  as the XZ dictionary size.  The dictionary size
    		can be specified as a percentage of the block size, or as an
    		absolute value.  The dictionary size must be less than or equal
    		to the block size and 8192 bytes or larger.  It must also be
    		storable in the xz header as either 2^n or as 2^n+2^(n+1).
    		Example dict-sizes are 75%, 50%, 37.5%, 25%, or 32K, 16K, 8K
    		etc.
    

    This differs from mksquashfs included in Arch Linux, which uses gzip by default! If you just go ahead and build the image using mksquashfs provided by your package manager, you will end up with a filesystem which is too large, and the build process will fail!

    
    $ mksquashfs -h
    SYNTAX:mksquashfs source1 source2 ...  dest [options] [-e list of exclude
    dirs/files]
    
    Filesystem build options:
    -comp 		select  compression
    			Compressors available:
    				gzip (default)
    
    (other options omitted)
    
    Compressors available and compressor specific options:
    	gzip (default)
    	  -Xcompression-level 
    		 should be 1 .. 9 (default 9)
    	  -Xwindow-size 
    		 should be 8 .. 15 (default 15)
    	  -Xstrategy strategy1,strategy2,...,strategyN
    		Compress using strategy1,strategy2,...,strategyN in turn
    		and choose the best compression.
    		Available strategies: default, filtered, huffman_only,
    		run_length_encoded and fixed
    	lzma (no options)
    	lzo
    	  -Xalgorithm 
    		Where  is one of:
    			lzo1x_1
    			lzo1x_1_11
    			lzo1x_1_12
    			lzo1x_1_15
    			lzo1x_999 (default)
    	  -Xcompression-level 
    		 should be 1 .. 9 (default 8)
    		Only applies to lzo1x_999 algorithm
    	lz4
    	  -Xhc
    		Compress using LZ4 High Compression
    	xz
    	  -Xbcj filter1,filter2,...,filterN
    		Compress using filter1,filter2,...,filterN in turn
    		(in addition to no filter), and choose the best compression.
    		Available filters: x86, arm, armthumb, powerpc, sparc, ia64
    	  -Xdict-size 
    		Use  as the XZ dictionary size.  The dictionary size
    		can be specified as a percentage of the block size, or as an
    		absolute value.  The dictionary size must be less than or equal
    		to the block size and 8192 bytes or larger.  It must also be
    		storable in the xz header as either 2^n or as 2^n+2^(n+1).
    		Example dict-sizes are 75%, 50%, 37.5%, 25%, or 32K, 16K, 8K
    		etc.
    

    At least the build process will fail and tell you the image is too large, instead of making an image which will brick your router...

    lzma
    Again I was wondering, why should I use the old version of LZMA included in the D-Link source, when Arch Linux ships which a much newer (and thus better) version of LZMA? It might occur to you, that I haven't learned my lesson yet from the previous experience with mksquashfs...

    The lzma included in D-Link's source:

    $ /opt/buildroot-gcc342/bin/lzma -h
    
    lzma 4.32.7 Copyright (C) 2005 Ville Koskinen
    Based on LZMA SDK 4.32 Copyright (C) 1999-2005 Igor Pavlov
    
    Usage: /opt/buildroot-gcc342/bin/lzma [flags and input files in any order]
      -c --stdout       output to standard output
      -d --decompress   force decompression
      -z --compress     force compression
      -k --keep         keep (don't delete) input files
      -f --force        force overwrite of output file and compress links
      -t --test         test compressed file integrity
      -S .suf  --suffix .suf   use suffix .suf on compressed files
      -q --quiet        suppress error messages
      -v --verbose      be verbose
      -h --help         print this message
      -L --license      display the license information
      -V --version      display version numbers of LZMA SDK and lzma
      -1 .. -2          fast compression
      -3 .. -9          good to excellent compression. -7 is the default.
         --fast         alias for -1
         --best         alias for -9 (usually *not* what you want)
    
      Memory usage depends a lot on the chosen compression mode -1 .. -9.
      See the man page lzma(1) for details.
    

    And lzma from Arch Linux:

    $ lzma -h
    Usage: lzma [OPTION]... [FILE]...
    Compress or decompress FILEs in the .xz format.
    
      -z, --compress      force compression
      -d, --decompress    force decompression
      -t, --test          test compressed file integrity
      -l, --list          list information about .xz files
      -k, --keep          keep (don't delete) input files
      -f, --force         force overwrite of output file and (de)compress links
      -c, --stdout        write to standard output and don't delete input files
      -0 ... -9           compression preset; default is 6; take compressor *and*
                          decompressor memory usage into account before using 7-9!
      -e, --extreme       try to improve compression ratio by using more CPU time;
                          does not affect decompressor memory requirements
      -T, --threads=NUM   use at most NUM threads; the default is 1; set to 0
                          to use as many threads as there are processor cores
      -q, --quiet         suppress warnings; specify twice to suppress errors too
      -v, --verbose       be verbose; specify twice for even more verbose
      -h, --help          display this short help and exit
      -H, --long-help     display the long help (lists also the advanced options)
      -V, --version       display the version number and exit
    
    With no FILE, or when FILE is -, read standard input.
    
    Report bugs to  (in English or Finnish).
    XZ Utils home page: 
    

    So, apart from the newer output looking much more like a standard GNU utility, you might have noticed that the older copy of lzma compresses with a default compression of -7 while the newer version compresses with a default compression of -6.

    If you think this doesn't make a difference, let me just tell you now, it does. A big one. The difference between -6 and -7 is the difference between a kernel that boots, and one that doesn't.

    This firmware was built with the D-Link SDK version of lzma and will boot:

    $ binwalk image/DAP1520A1_FW106B04.bin 
    
    DECIMAL       HEXADECIMAL     DESCRIPTION
    --------------------------------------------------------------------------------
    0             0x0             uImage header, header size: 64 bytes, header CRC: 0x46768407, created: 2016-03-05 22:33:15, image size: 909272 bytes, Data Address: 0x80000000, Entry Point: 0x8000C310, data CRC: 0x4993B2D9, OS: Linux, CPU: MIPS, image type: OS Kernel Image, compression type: lzma, image name: "Linux Kernel Image"
    64            0x40            LZMA compressed data, properties: 0x5D, dictionary size: 33554432 bytes, uncompressed size: 2798288 bytes
    983040        0xF0000         Squashfs filesystem, little endian, version 4.0, compression:xz, size: 3445784 bytes, 655 inodes, blocksize: 65536 bytes, created: 2016-03-05 22:33:20
    

    This firmware was built with the Arch Linux version of lzma and won't boot:

    $ binwalk image/DAP1520A1_FW106B04.bin 
    
    DECIMAL       HEXADECIMAL     DESCRIPTION
    --------------------------------------------------------------------------------
    0             0x0             uImage header, header size: 64 bytes, header CRC: 0x7A57558F, created: 2016-03-07 20:41:46, image size: 908147 bytes, Data Address: 0x80000000, Entry Point: 0x8000C310, data CRC: 0x8E0F6C03, OS: Linux, CPU: MIPS, image type: OS Kernel Image, compression type: lzma, image name: "Linux Kernel Image"
    983040        0xF0000         Squashfs filesystem, little endian, version 4.0, compression:xz, size: 3451428 bytes, 653 inodes, blocksize: 65536 bytes, created: 2016-03-07 20:41:49
    

    So, what exactly happens when you flash this image to the device? Does it do some verification before flashing and stop you? Does it flash the image, and then when Image 1 fails to boot it boots the linux4b image and start rootfsb so you can recover the device?

    Not quite...

    Image1 Try Counter --> 0
    
    Image1: OK Image2: OK
    Both images are OK!!!
    
    =================================================
    
    Please choose the operation: 
       1: Load system code to SDRAM via TFTP. 
       2: Load system code then write to Flash via TFTP. 
       3: Boot system code via Flash (default).
       4: Entr boot command line interface.
       7: Load Boot Loader code then write to Flash via Serial. 
       9: Load Boot Loader code then write to Flash via TFTP. 
     1  0 
       
    3: System Boot system code via Flash.
    ## Booting image at bc050000 ...
    raspi_read: from:50000 len:40 
       Image Name:   Linux Kernel Image
       Image Type:   MIPS Linux Kernel Image (lzma compressed)
       Data Size:    908132 Bytes = 886.8 kB
       Load Address: 80000000
       Entry Point:  8000c310
    raspi_read: from:50040 len:ddb64 
       Verifying Checksum ... OK
       Uncompressing Kernel Image ... LZMA ERROR 1 - must RESET board to recover
    

    So, no. No verification of the validity of the kernel in the update before flashing. And no, it won't boot from Image 2. You will just see this error, over and over, while the device resets. You might think that Image1 Try Counter would increment, and after a threshold it would boot into the recovery environment, but no. Congratulations, you are now the proud owner of a brick. Get out your SPI flashing tool, because there's no other way around this disaster.

    This does beg the question, how do you get the device to boot into Image 2? Well, after the LZMA compression snafu on the kernel, I thought I would save some time and just flash the vmlinuz.ub file created by the build script to flash and be done with it... nope!

    
    Check image validation:
    Image1 Header Magic Number --> OK
    Image2 Header Magic Number --> OK
    Image1 Header Checksum --> OK
    Image2 Header Checksum --> OK
    Image1 Data Checksum --> raspi_read: from:50040 len:de000 
    Failed
    Image2 Data Checksum --> raspi_read: from:4f0040 len:ca8f4 
    OK
    Image1 Stable Flag --> Not stable
    Image1 Try Counter --> 0
    
    Image1: Broken Image2: OK
    Only Image1 is borken!!
    
    =================================================
    
    Please choose the operation: 
       1: Load system code to SDRAM via TFTP. 
       2: Load system code then write to Flash via TFTP. 
       3: Boot system code via Flash (default).
       4: Entr boot command line interface.
       7: Load Boot Loader code then write to Flash via Serial. 
       9: Load Boot Loader code then write to Flash via TFTP. 
     1  0 
       
    3: System Boot system code via Flash.
    ## Booting image at bc4f0000 ...
    raspi_read: from:4f0000 len:40 
       Image Name:   Linux Kernel Image
       Image Type:   MIPS Linux Kernel Image (lzma compressed)
       Data Size:    829684 Bytes = 810.2 kB
       Load Address: 80000000
       Entry Point:  8000c310
    raspi_read: from:4f0040 len:ca8f4 
       Verifying Checksum ... OK
       Uncompressing Kernel Image ... OK
    No initrd
    ## Transferring control to Linux (at address 8000c310) ...
    ## Giving linux memsize in MB, 64
    
    Starting kernel ...
    
    
    LINUX started...
    
     THIS IS ASIC
    Linux version 2.6.36.x ([email protected]) (gcc version 3.4.2) #1 Thu Sep 26 16:47:12 CST 2013
    

    Couple of things to note here:

    1. Only Image1 is borken!!
    2. The kernel in Image 2 is much older, and was built on a different host, than the kernel in Image 1 from D-Link

    When you do flash a working firmware back onto the router, you get a surprise when it boots. Because Image1 is borken!! the device rewrites all the nvram variables to their defaults.

    
    init NVRAM_SPACE from mtdblock size
    init nvram memory map size: 0x10000 order of pages: 0x4
    nvram module init:
    	/dev/nvram major number 225 glues to mtd: "nvram" size: 0x00010000
    	nvram_space: 0x00010000 mapped via mmap(2)
    openfile :/etc/sysinfo
    openfile :/etc/nvram.default
    nvram_sanity_check: restore key: uplink_set_by_user="0"
    nvram_sanity_check: restore key: language="default"
    nvram_sanity_check: restore key: ap_ipv6_wan_specify_dns="0"
    nvram_sanity_check: restore key: ap_ipv6_autoconfig_secondary_dns=""
    nvram_sanity_check: restore key: ap_ipv6_autoconfig_primary_dns=""
    nvram_sanity_check: restore key: ap_ipv6_autoconfig_dns_enable="0"
    nvram_sanity_check: restore key: ap_ipv6_static_secondary_dns=""
    nvram_sanity_check: restore key: ap_ipv6_static_primary_dns=""
    nvram_sanity_check: restore key: ap_ipv6_static_default_gw=""
    nvram_sanity_check: restore key: ap_ipv6_static_prefix_length=""
    nvram_sanity_check: restore key: ap_ipv6_static_lan_ip=""
    nvram_sanity_check: restore key: ap_ipv6_wan_proto="ipv6_autoconfig"
    nvram_sanity_check: restore key: pure_support_url="http://support.dlink.com/products/view.asp?productid=DAP-1520"
    nvram_sanity_check: restore key: pure_reboot_page="reboot.htm"
    nvram_sanity_check: restore key: pure_parental_url=""
    nvram_sanity_check: restore key: pure_block_url=""
    nvram_sanity_check: restore key: pure_wireless_url_new="/Wireless.htm"
    nvram_sanity_check: restore key: pure_wireless_url="/wireless.htm"
    nvram_sanity_check: restore key: pure_presentation_url="/Device_Info.htm"
    nvram_sanity_check: restore key: pure_model_description="Wireless Repeater"
    nvram_sanity_check: restore key: pure_vendor_name="D-Link"
    nvram_sanity_check: restore key: pure_device_name="D-Link Systems DAP-1520"
    nvram_sanity_check: restore key: pure_type_new="WiFiAccessPoint"
    nvram_sanity_check: restore key: pure_type="Repeater"
    nvram_sanity_check: restore key: default_downlink_ssid="1"
    nvram_sanity_check: restore key: wlan1_wps_wizard="0"
    nvram_sanity_check: restore key: setup_wizard_ap="1"
    nvram_sanity_check: restore key: log_response_type="system|debug|attack|dropped|notice"
    nvram_sanity_check: restore key: log_current_page="0"
    nvram_sanity_check: restore key: log_total_page="0"
    nvram_sanity_check: restore key: log_per_page="10"
    nvram_sanity_check: restore key: log_notice="1"
    nvram_sanity_check: restore key: log_dropped_packets="0"
    nvram_sanity_check: restore key: log_attacks="1"
    nvram_sanity_check: restore key: log_debug_information="0"
    nvram_sanity_check: restore key: log_system_activity="1"
    nvram_sanity_check: restore key: syslog_server="0/0.0.0.0"
    nvram_sanity_check: restore key: time_daylight_offset="3600"
    nvram_sanity_check: restore key: time_daylight_saving_end_time="1"
    nvram_sanity_check: restore key: time_daylight_saving_end_day_of_week="1"
    nvram_sanity_check: restore key: time_daylight_saving_end_week="2"
    nvram_sanity_check: restore key: time_daylight_saving_end_month="11"
    nvram_sanity_check: restore key: time_daylight_saving_start_time="1"
    nvram_sanity_check: restore key: time_daylight_saving_start_day_of_week="1"
    nvram_sanity_check: restore key: time_daylight_saving_start_week="3"
    nvram_sanity_check: restore key: time_daylight_saving_start_month="3"
    nvram_sanity_check: restore key: time_daylight_saving_enable="0"
    nvram_sanity_check: restore key: ntp_sync_interval="168"
    nvram_sanity_check: restore key: ntp_default_server="ntp1.dlink.com,ntp.dlink.com.tw"
    nvram_sanity_check: restore key: ntp_server=""
    nvram_sanity_check: restore key: time_zone_area="4"
    nvram_sanity_check: restore key: time_zone="-128"
    nvram_sanity_check: restore key: ntp_client_enable="0"
    nvram_sanity_check: restore key: session_timeout="180"
    nvram_sanity_check: restore key: graph_enable="none"
    nvram_sanity_check: restore key: system_time="2011/01/01/00/00/00"
    nvram_sanity_check: restore key: serial_number="none"
    nvram_sanity_check: restore key: model_url="http://support.dlink.com"
    nvram_sanity_check: restore key: model_name="D-Link Repeater"
    nvram_sanity_check: restore key: manufacturer_url="http://www.dlink.com"
    nvram_sanity_check: restore key: manufacturer="D-Link"
    nvram_sanity_check: restore key: friendlyname="DAP-1520"
    nvram_sanity_check: restore key: model_number="DAP-1520"
    nvram_sanity_check: restore key: hostname="DAP-1520"
    nvram_sanity_check: restore key: wlan1_11n_protection="auto"
    nvram_sanity_check: restore key: wlan1_wps_enable="1"
    nvram_sanity_check: restore key: wlan1_psk_pass_phrase="1234567890"
    nvram_sanity_check: restore key: wlan1_psk_cipher_type="both"
    nvram_sanity_check: restore key: wlan1_wep_display="hex"
    nvram_sanity_check: restore key: wlan1_wep128_key="00000000000000000000000000"
    nvram_sanity_check: restore key: wlan1_wep64_key="0000000000"
    nvram_sanity_check: restore key: wlan1_security="disable"
    nvram_sanity_check: restore key: wlan1_ssid=""
    nvram_sanity_check: restore key: wlan_repeater_mode="1"
    nvram_sanity_check: restore key: wlan0_disable_wps_pin="1"
    nvram_sanity_check: restore key: wlan0_wps_configured_mode="5"
    nvram_sanity_check: restore key: wlan0_wps_enable="1"
    nvram_sanity_check: restore key: wlan0_disablecoext="0"
    nvram_sanity_check: restore key: wlan0_rxchainmask="3"
    nvram_sanity_check: restore key: wlan0_txchainmask="3"
    nvram_sanity_check: restore key: wlan0_gkey_rekey_time="3600"
    nvram_sanity_check: restore key: wlan0_11n_protection="auto"
    nvram_sanity_check: restore key: wlan0_wmm_enable="1"
    nvram_sanity_check: restore key: wlan0_short_gi="1"
    nvram_sanity_check: restore key: wlan0_partition="0"
    nvram_sanity_check: restore key: wlan0_dtim="1"
    nvram_sanity_check: restore key: wlan0_fragmentation="2346"
    nvram_sanity_check: Raeth v3.0 (reTaskletst,SkbRecycleo)
    nvram_sanity_check: restore key: wlan0_beacon_interval="100"
    nvram_sanity_check: restore key: wlan0_txpower="100"
    nvram_sanity_check: restore key: wlan0_psk_cipher_type="both"
    nvram_sanity_check: restore key: wlan0_wep_display="hex"
    nvram_sanity_check: restore key: wlan0_wep128_key="00000000000000000000000000"
    nvram_sanity_check: restore key: wlan0_wep64_key="0000000000"
    nvram_sanity_check: restore key: wlan0_ssid_broadcast="1"
    nvram_sanity_check: restore key: wlan0_dot11_mode="11bgn"
    nvram_sanity_check: restore key: wlan0_auto_channel_enable="1"
    nvram_sanity_check: restore key: wlan0_channel="6"
    nvram_sanity_check: restore key: wlan0_enable="1"
    nvram_sanity_check: restore key: wlan0_5g_fragmentation="2346"
    nvram_sanity_check: restore key: wlan0_5g_rts_threshold="2347"
    nvram_sanity_check: restore key: wlan0_5g_dfs_enable="0"
    nvram_sanity_check: restore key: wlan0_5g_11n_protection="adevice eth2 entered promiscuous mode
    uto"
    nvram_sanity_check: restore key: wlan0_5g_wep128_key="00000000000000000000000000"
    nvram_sanity_check: restore key: wlan0_5g_wep64_key="0000000000"
    nvram_sanity_check: restore key: wlan0_5g_psk_cipher_type="both"
    nvram_sanity_check: restore key: wlan0_5g_wep_display="hex"
    nvram_sanity_check: restore key: wlan0_5g_wmm_enable="1"
    nvram_sanity_check: restore key: wlan0_5g_txpower="100"
    nvram_sanity_check: restore key: wlan0_5g_dtim="1"
    nvram_sanity_check: restore key: wlan0_5g_beacon_interval="100"
    nvram_sanity_check: restore key: wlan0_5g_auto_channel_enable="1"
    nvram_sanity_check: restore key: wlan0_5g_channel="36"
    nvram_sanity_check: restore key: wlan0_5g_dot11_mode="11anac"
    nvram_sanity_check: restore key: dhcpc_enable="1"
    nvram_sanity_check: restore key: ap_device_name="dlinkap"
    nvram_sanity_check: restore key: ap_secondary_dns="0.0.0.0"
    nvram_sanity_check: restore key: ap_primary_dns="0.0.0.0"
    nvram_sanity_check: restore key: ap_gateway="0.0.0.0"
    nvram_sanity_check: restore key: ap_netmask="255.255.255.0"
    nvram_sanity_check: restore key: ap_ipaddr="192.168.0.50"
    nvram_sanity_check: restore key: lan_bridge="br0"
    nvram_sanity_check: restore key: lan_eth="eth2"
    nvram_sanity_check: restore key: admin_password=""
    nvram_sanity_check: restore key: admin_username="admin"
    

    Solid defaults there, D-Link. I think this is the first device I've ever encountered where the admin password was actually blank. I setup the device initially, and then it rebooted and asked me for a password to login. Even working in IT, I never thought to try an empty password. I mean, who does that?! D-Link does that.

    And just while writing this I realized that I can look at the nvram defaults any time I want to in /etc/nvram.defaults. This is why you use the 15 minute rule, people.

    Below is a firmware with nc running on port 8023 if you have a DAP-1520 and you want to poke around the D-Link firmware. Telnet asks for a username and password, and none of the combinations I could think of let me login.

    nc 192.168.0.50 8023

    Enjoy your root shell!

    Firmware DAP1520A1_FW106B04.bin (gzip compressed) with nc backdoor.
    md5sum: 31397369d0631183c3823d9933bede5f
    sha1sum: 2951f4e36b05014cbc327acf5c9d6e860ac2f0a5
    sha256sum: 6dd416c6f26e17f059dcc531e2a882a64e3af0594bd3720da669af631c34e50b