Tag Archives: fujitsu tx140 s2

Fujitsu iRMC S4 License

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A few years ago we looked at iRMC S4 on the Fujitsu TX140 S2. iRMC S4 provides typical remote management features that you would expect to find in a BMC: remote power control, sensor monitoring and alerting, hardware inventory, and boot order over-ride/selection. Some additional features like the remote KVM and remote media require a license key.

Licensed IPMI features are not new and other vendors, such as Supermicro, have had their IPMI license reverse engineered.

Fujitsu are a somewhat niche vendor when it comes to servers, and to date I am not aware that anyone has publicly reverse engineered the iRMC S4 license.

They say a picture is worth a thousand words, so we will start with a diagram

iRMC S4 license contents

An iRMC S4 license has four distinct fields

  1. Header/magic: 4 bytes (iRMC)
  2. Features to be enabled by the license (bitmask): 4 bytes
  3. Type of license (temporary or permanent): 4 bytes
  4. CRC32 of the system serial number: 4 bytes

The above data is encrypted using AES-128, and the output is base32 encoded with hyphens every 4 characters.

For example, here is an iRMC S4 license (enabling KVM and remote media) for an RX chassis with the serial number YLNS012345:

ZKAF-Z5EG-PL5G-6GFR-YEG6-CKGM-KQ

And the actual license contents:

69524d43 0300000 0ffffff05 2e4dbb51

Licensed features in iRMC S4 include:

  • Remote KVM
  • Remote media
  • eLCM

Feature bit 1 is for KVM, bit 2 remote media, and bit 3 seems to be for eLCM (eLCM appears to only be available on some models).

Installing an iRMC S4 license on a TX chassis

Back in 2014, Fujitsu changed the iRMC S4 licensing to be “node-locked”, which means that a license is tied to a specific server and cannot be transferred. The installation of a volume license is not possible after 2015-01-01 00:00:00.

iRMC S4 tracks the “Power on Hours (PoH)” of the chassis, and it appears that there is the capability to generate a temporary license which will expire after a certain number of Power on Hours is reached, probably to provide customers with time to evaluate the value proposition of purchasing iRMC licenses.

iRMC S4 time limited license

If you are reading this, then you are probably not interested in generating temporary licenses. Setting the field to 0xffffff00 for a TX chassis and 0xffffff05 for an RX chassis will result in a permanent license.

Now that we have covered the fields in an unencrypted iRMC S4 license, it will be obvious that the example license ZKAF-Z5EG-PL5G-6GFR-YEG6-CKGM-KQ is not simply the base32 encoded binary license data.

Unlike Supermicro, Fujitsu use a static HMAC message and key to create an HMAC-SHA1 hash, the first 16 bytes of which are used as the key for AES-128. The AES encrypted data is then base32 encoded and the output is the iRMC license you install via the web interface.

I will not be disclosing Fujitsu’s HMAC key and AES IV here, but suffice to say you can download and unpack the iRMC firmware from Fujitsu and find the values in /usr/local/lib/libfts_license.so.1.12.1. Thanks Fujitsu!

For anyone interested in reverse engineering the iRMC S4 license validation themselves:

  • the HMAC key and message are used in lkeyInitCipherKey in libfts_license
  • the AES IV is used in decrypt_with_license in libfts_license

libfts_license in Ghidra, showing decompiled function and hexdump

Anyone looking for a simpler solution, a proof-of-concept for python is here. Note that you need to provide the correct HMAC/AES values obtained from libfts_license, you do not need Ghidra for this, you can do it with a simple hexdump utility.

To anyone wondering, the license logic from iRMC S4 is not applicable to older iRMC platforms such as iRMC S2 or iRMC S3.

However, the license logic appears to be unchanged between iRMC S4 and S5. Hardware with iRMC S5 is too expensive to justify purchasing to verify this, but maybe someone will leave a comment as to whether the license logic described here is still applicable to iRMC S5.

Edit: An anonymous reader has written to say that the logic is unchanged for iRMC S5 ✨

Fujitsu iRMC S4 on the TX140 S2

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Fujitsu servers come with a remote management solution called iRMC S4 (newer models have iRMC S5). iRMC S4 and S5 are like other lights-out remote management solutions from HP (iLO) or Dell (iDRAC) which comprises a baseband management controller firmware along with other software utilities to remotely configure and manage servers. Importantly though, iRMC S4 runs Linux.

Before we get into the hardware of iRMC S4, let us examine the firmware update process. iRMC S4 follows a pretty typical BMC firmware update process: Fujitsu’s support website offers firmware downloads, and the iRMC web management interface allows you to upload the update which is then written to the inactive firmware slot.

As is common for enterprise hardware, there is no rollback protection, so you can downgrade the installed firmware to previous versions. I did not extensively test this functionality though, so there may be limits to how far you can downgrade as the firmware modifies the persistent conf partition (which is not redundant).

Running binwalk against the update file for the TX140 S2, we can immediately see that it is not encrypted:

$ binwalk FTS_TX140S2D3239iRMCKronos4FirmwareUpdatefo_TX140S20960Fsdr0344_1233853.BIN 

DECIMAL       HEXADECIMAL     DESCRIPTION
--------------------------------------------------------------------------------
148820        0x24554         U-Boot version string, "U-Boot 1.1.6 (Sep 22 2015 - 17:25:45)"
150076        0x24A3C         CRC32 polynomial table, little endian
184888        0x2D238         CRC32 polynomial table, little endian
589824        0x90000         uImage header, header size: 64 bytes, header CRC: 0x2658385F, created: 2020-04-01 11:24:03, image size: 27389952 bytes, Data Address: 0x0, Entry Point: 0x0, data CRC: 0x6B45479A, OS: Linux, CPU: ARM, image type: RAMDisk Image, compression type: none, image name: ""
589888        0x90040         CramFS filesystem, little endian, size: 27389952, version 2, sorted_dirs, CRC 0x6745F599, edition 0, 15794 blocks, 4707 files
27983936      0x1AB0040       uImage header, header size: 64 bytes, header CRC: 0x27056A57, created: 2019-11-04 16:46:29, image size: 3042664 bytes, Data Address: 0x80808000, Entry Point: 0x80808000, data CRC: 0x222093D7, OS: Linux, CPU: ARM, image type: OS Kernel Image, compression type: none, image name: "Linux-3.14.17-ami"
27984000      0x1AB0080       Linux kernel ARM boot executable zImage (little-endian)
28002116      0x1AB4744       gzip compressed data, maximum compression, from Unix, last modified: 1970-01-01 00:00:00 (null date)
31129600      0x1DB0000       CramFS filesystem, little endian, size: 45056, version 2, sorted_dirs, CRC 0x52551191, edition 0, 31 blocks, 12 files

As far as I have been able to determine, here is the firmware layout of iRMC S4 on the TX140 S2:

00000000:0008ffff uboot1
00090000:01aaf040 root1 # cramfs1
01ab0040:01daffff zImage1
01db0000:01dc0000 platform1 # sdr1
01e24554:01e8ffff uboot2
01e90000:038af040 root2 # cramfs2
038b0040:03baffff zImage2
03bb0000:03bc0000 platform2 # sdr2
03c00000:03ff0000 conf
03ff0000:03ffffff fru

These correspond to the lower and higher firmware slots in iRMC S4, and ensure that the firmware you are updating is not the currently running firmware.

So, could our way into iRMC S4 be as easy as modifying the cramfs from the firmware update?

Unfortunately, no. The update is signed and the signature is checked by /usr/local/bin/flasher against an RSA-1024 public key located on the conf partition prior to overwriting:

-----BEGIN PUBLIC KEY-----
MIGfMA0GCSqGSIb3DQEBAQUAA4GNADCBiQKBgQCdgO/cGwthsFEZLuohVB5DNvU/
LolrQobsNASL4Sc+uzn8PsULIPiG0v3zhR8zCwlChmF/umVvk1gxKy5cAY0Bj3oo
cUhXwHf4t2ty+2ZY+p975Yg6YonQJSTKVPVfBlk/9PqNRj/Ih5P3zqd80YxAoKhX
i77qhLxjehHLsRSP2QIDAQAB
-----END PUBLIC KEY-----

Attempting to modify and repack cramfs results in the following output to the UART:

[1533 : 1533 INFO]VerifyImage
Signature Verification Failure
[1533 : 1533 CRITICAL][utils.c:1241]Signature verification failed 
[1533 : 1533 CRITICAL][utils.c:1522]Encrypted hash of Image and the actual contents of rom.ima does not match

With our software-only modification route looking grim, it is time to move on into the realm of the evil maid.

On the TX140 S2 the BMC UART (38400n8) has been routed to pads, located just below PCIe slot 2, which are easily soldered to:

BMC UART connections on a Fujitsu TX140 S2 motherboard
BMC UART on the TX140 S2 (D3239) motherboard

To stop the default boot sequence, press Escape within 2 seconds:

U-Boot 1.1.6 (Jun 20 2013 - 09:09:05)

DRAM:  247 MB
Fast clk is set
Found SPI Chip Macronix MX66L51235F 
Flash: 64 MB
Net:   pilot_eth0, pilot_eth1
Hit Esc key to stop autoboot:  0 
------ Boot Options-------
        0. Normal Boot
        1. Diagnostics
        2. Remote Recovery
        3. Management Console
        4. Raw Console
Select Boot Option:

The GPL source code for iRMC S4 was requested in December 2020, and at the time of writing Fujitsu had not provided the source code. Without the source code for u-boot, it is difficult to determine if there are any routes that could lead to easy exploitation.

Getting a root console is relatively straightforward with soldering or a chip jig. If you use a jig, you will need very steady hands as flashrom requires 20-30 minutes to write and verify the 27MB cramfs region.

512MBit MXIC flash of the TX140 S2 iRMC S4 BMC

Lucky me, Fujitsu engineers considered physical modification of the iRMC S4 firmware out of scope, and there is no secure boot or signature verification of the cramfs on flash.

Since we can manipulate cramfs, we can bypass the stock Fujitsu shell and replace /usr/local/bin/remman with a symlink to /bin/sh and SSH as the admin user. This is not particularly useful though, as the admin user is not root sysadmin, and the busybox that Fujitsu ship is lacking the su applet, so there’s no way to easily escalate your privileges from admin to sysadmin once logged in.

~ $ id
uid=1002(admin) gid=501(ipmi) groups=501(ipmi),504(lanoem),510(serialoem),528(iRMCsettings),529(RemoteStorage),530(UserAccounts),531(VideoRedirection),532(CfgConnectionBlade),535(RemoteManager)

The uid 0 account is not called root, but rather sysadmin with the password superuser:

sysadmin:$1$A17c6z5w$5OsdHjBn1pjvN6xXKDckq0:18627:0:99999:7:::

The sysadmin account is not visible in the iRMC web interface and, as far as I can tell, the password cannot be changed (unless you physically modify the contents of cramfs). I believe the account is leftover from the SDK that iRMC S4 appears to be based on.

All my attempts to login as sysadmin via SSH or uart with the default remman shell were unsuccessful, so it doesn’t appear to be a security risk out of the box.

However, once you have replaced /usr/local/bin/remman with a symlink to /bin/sh it is possible to login as the sysadmin user and enjoy root access to your iRMC S4.