I have an aging Dell T710 that I bought a number of years ago. I use it to offload long running processes, handle file sharing, shared services, jails and so on. It's been running FreeBSD for a couple of years since I moved away from Linux.
Like most server-class hardware this tower is particularly loud. Dell shipped it with pulse width modulated fans that are anything but quiet and thanks to the iDRAC6 Express software that runs on a WPCM450 integrated baseboard management controller (BMC) the fan control & throttling makes it sound like a jet is taking off. That's fine if you have somewhere to put it but we've moved to a small apartment and it has to sit in our office. As we're fans of hearing ourselves think (pun intended) I needed some way to wrestle control away from the default iDRAC firmware.
The WPCM450 runs a version of Busybox Linux on an ARM processor. As you would expect, Dell has heavily customized this software and provides access to it via a web interface, Telnet, SSH, RAC, IPMI or Serial interface to RAC/IPMI. None of these options offer the controls we're looking for and the SSH/Telnet options are locked down to the iDRAC SM-CLP command line interface. In short, Dell has turned an otherwise very useful out-of-band management tool into a glorified toaster oven.
Previous versions of the Dell BMC have been reverse engineered by others however the Dell T710 is an 11th generation server so sadly we can't use those methods.
If you follow these instructions you may brick your iDRAC, cause damage to your hardware, open security holes, cause future upgrades to go awry and make small children cry. I take zero responsibility for anything that you do to your own systems. You will certainly void Dell's warranty for whatever that's worth.
Before we get started
Make sure you have Telnet access enabled under the Web GUI at iDRAC Settings > Network/Security > Services. Alternatively if you have racadm access, either through SSH to iDRAC or otherwise, you can enable Telnet by issuing the following command:
$ racadm config -g cfgSerial -o cfgSerialTelnetEnable 1
You may need to adjust the racadm command appropriately if you are accessing it indirectly.
If you have just set up your iDRAC you should be able to gain access using the default root user & password calvin
Also, you'll need to obtain an up-to-date copy of the iDRAC firmware. You can use ESM_Firmware_9GJYW_LN32_2.90_A00.BIN or ESM_Firmware_9GJYW_WN32_2.90_A00.EXE with the latter being a bit easier to open since it's just a ZIP file. I successfully extracted the firmware from the .BIN file but it was a bit more work as I run FreeBSD and not Linux. You'll find the firmware under
Exploring firmimg.d6 with binwalk
Binwalk helps us determine how the firmware image is set up and gives us the addresses that we can use to split it up into workable sections. Be mindful that some of these addresses are spurious so we can't use binwalk's automated extraction feature.
Scan Time: 2017-11-01 13:02:06 Target File: /usr/home/matt/tmp/firmimg.d6 MD5 Checksum: 24a113b5baae30dfac9a888d69a09784 Signatures: 344 DECIMAL HEXADECIMAL DESCRIPTION -------------------------------------------------------------------------------- 512 0x200 uImage header, header size: 64 bytes, header CRC: 0x14BBDCB0, created: 2017-07-24 10:04:17, image size: 4479904 bytes, Data Address: 0x8000, Entry Point: 0x8000, data CRC: 0xD9EEF7BB, OS: Linux, CPU: ARM, image type: OS Kernel Image, compression type: none, image name: "arm-linux" 103296 0x19380 gzip compressed data, maximum compression, from Unix, last modified: 2017-07-24 10:00:07 639113 0x9C089 Certificate in DER format (x509 v3), header length: 4, sequence length: 5472 1057005 0x1020ED Certificate in DER format (x509 v3), header length: 4, sequence length: 4696 1090593 0x10A421 Certificate in DER format (x509 v3), header length: 4, sequence length: 4812 1722433 0x1A4841 Certificate in DER format (x509 v3), header length: 4, sequence length: 517 2090901 0x1FE795 Certificate in DER format (x509 v3), header length: 4, sequence length: 1 2142644 0x20B1B4 SHA256 hash constants, little endian 2737477 0x29C545 Certificate in DER format (x509 v3), header length: 4, sequence length: 4099 3060125 0x2EB19D Certificate in DER format (x509 v3), header length: 4, sequence length: 5512 3065589 0x2EC6F5 Certificate in DER format (x509 v3), header length: 4, sequence length: 1428 3071865 0x2EDF79 Certificate in DER format (x509 v3), header length: 4, sequence length: 1404 3097813 0x2F44D5 Certificate in DER format (x509 v3), header length: 4, sequence length: 5568 3104893 0x2F607D Certificate in DER format (x509 v3), header length: 4, sequence length: 1456 3104937 0x2F60A9 Certificate in DER format (x509 v3), header length: 4, sequence length: 1452 3104981 0x2F60D5 Certificate in DER format (x509 v3), header length: 4, sequence length: 1476 3209149 0x30F7BD Certificate in DER format (x509 v3), header length: 4, sequence length: 4354 3395109 0x33CE25 Certificate in DER format (x509 v3), header length: 4, sequence length: 0 3457388 0x34C16C Linux kernel version "22.214.171.124 (root@BDCCBFV24.blr.amer.dell.com) (gcc version 3.4.5) #1 PREEMPT Mon Jul 24 10:04:06 UTC 2017" 3474457 0x350419 Neighborly text, "neighborighbor_position" 3474489 0x350439 Neighborly text, "neighbor_positioncheck_internal_node" 3474518 0x350456 Neighborly text, "neighbor_positione_starts" 3475888 0x3509B0 Neighborly text, "neighbor_in_cache" 3476008 0x350A28 Neighborly text, "neighborscheck_balance" 3476211 0x350AF3 LZMA compressed data, properties: 0xC0, dictionary size: 2097152 bytes, uncompressed size: 5242880 bytes 3476247 0x350B17 LZMA compressed data, properties: 0xC0, dictionary size: 524288 bytes, uncompressed size: 262144 bytes 3604728 0x3700F8 CRC32 polynomial table, little endian 3993948 0x3CF15C Neighborly text, "neighbortion !(dest NULL || src NULL) failed at fs/reiserfs/do_balan.c:%i:%s: vs-12305: source or destination buffer is 0 (src=%p," 4000156 0x3D099C Neighborly text, "neighboring item failed at fs/reiserfs/do_balan.c:%i:%s: PAP-12125: no place for paste. pos_in_item=%d" 4010094 0x3D306E Neighborly text, "neighbor (%b %z) is not in the tree(n_counter < FIRST_PATH_ELEMENT_OFFSET) failed at fs/reiserfs/fix_node.c:%i:%s: PAP-8180: invalid path length" 4010592 0x3D3260 Neighborly text, "neighbor_father.path_length < FIRST_PATH_ELEMENT_OFFSET) failed at fs/reiserfs/fix_node.c:%i:%s: PAP-8192: path length is too sm at fs/reiserfs/fix_node.c:%i:%s: PAP-8192: path length is too small" 4011881 0x3D3769 Neighborly text, "neighbor&& PATH_OFFSET_POSITION(p_s_tb->tb_path, n_path_offset) >= B_NR_ITEMS(p_s_bh)) failed at fs/reiserfs/fix_node.c:%i:%s: PAP-8295:" 4012322 0x3D3922 Neighborly text, "neighbor (%d != %d - %d)gative or zero reference counter for buffer %s[%d] (%b)" 4026862 0x3D71EE Neighborly text, "neighbor, it must have free_space==0 (not %lu) assertion !(op_is_left_mergeable(&(ih->ih_key), src->b_size)) failed at fs/reiserfs/lbalance.c:%i:%s: vs-10190: bad mergeabilit" 4109761 0x3EB5C1 Unix path: /proc/fs/cifs/SecurityFlags 4110202 0x3EB77A Unix path: /proc/fs/cifs/PacketSigningEnabled to be on 4119170 0x3EDA82 Unix path: /proc/fs/cifs/LookupCacheEnabled to 0 4452031 0x43EEBF LZMA compressed data, properties: 0xC0, dictionary size: 2097152 bytes, uncompressed size: 4194304 bytes 4452055 0x43EED7 LZMA compressed data, properties: 0xC0, dictionary size: 2097152 bytes, uncompressed size: 6291456 bytes 4466660 0x4427E4 LZMA compressed data, properties: 0xC8, dictionary size: 33554432 bytes, uncompressed size: 2048 bytes 4480512 0x445E00 CramFS filesystem, little endian, size: 52203520 version 2 sorted_dirs CRC 0x977DA80B, edition 0, 28576 blocks, 3207 files 56795116 0x3629FEC U-Boot version string, "U-Boot 1.2.0 (Jul 24 2017 - 09:59:41) Avocent (1.13.8) Whoville" 56795728 0x362A250 CRC32 polynomial table, little endian
Split up firmware into logical sections
We'll modify two of the resulting files and use the others to put Humpty back together again.
Note that the addresses used below only apply to the 9GJYW 2.90 A00 ESM package. Any other package/firmware image is likely to have different addresses.
## This is the header file containing CRC32 checksums (we'll need to modify it accordingly) dd if=firmimg.d6 of=01_header bs=1 count=512 ## Back this up just-in-case cp 01_header 01_header_VIRGIN ## Will be used later to reconstruct the firmware image dd if=firmimg.d6 of=02_before_cramfs bs=1 skip=512 count=$((4480512-512)) ## This is the Linux Compressed ROM image that we need to modify dd if=firmimg.d6 of=03_cramfs bs=1 skip=4480512 count=52203520 ## Will be used later to reconstruct the firmware image dd if=firmimg.d6 of=04_after_cramfs bs=1 skip=$((4480512+52203520))
Unpack CramFS filesystem and make changes
Do this as root to preserve permissions. Then make modifications to image to gain shell access and finally repack for use.
$ cramfsck -x cramfs 03_cramfs ## Otherwise we can't su to root later on $ chmod u+s cramfs/bin/busybox
etc/sysapps_script/S_7015_telnetd_app.sh as follows to allow backdoor access via netcat:
--- cramfs_VIRGIN/etc/sysapps_script/S_7015_telnetd_app.sh 1969-12-31 17:00:00.000000000 -0700 +++ cramfs/etc/sysapps_script/S_7015_telnetd_app.sh 2017-11-01 11:39:57.461625000 -0600 @@ -15,6 +15,7 @@ # test if the variable is null is true if [ ] && [ == "true" ]; then -p -t + /bin/nc -l -p 2323 -e /bin/bash & fi touch /var/run/utmp else
$ mkcramfs cramfs 03_cramfs_MODIFIED
Update header checksums
The Dell firmware upgrade process uses checksums to verify "partition" content so the header needs to be updated to reflect changes made. Your checksums will surely be different so don't reuse those below. They are for example only.
I have used this Perl script to generate the CRC32 hex digests as required by the firmware header. Save as
~/bin/crc32 and execute as seen below.
Note that checksums are stored in reverse (little endian) order so they effectively "read backwards" when viewed from a hex editor.
$ crc32 03_cramfs_MODIFIED f00d648a ## Use whatever hex editor strikes your fancy (hte, radare2, etc.) ## Modify 34h, 35h, 36h and 37h. This is the cram "partition" checksum. $ hte 01_header ## Split out the actual header content from the header's own CRC32 $ dd if=01_header bs=1 skip=4 of=header_for_crc32 $ crc32 header_for_crc32 7b4bb3b9 ## Use whatever hex editor strikes your fancy (hte, radare2, etc.) ## Modify 0h, 1h, 2h and 3h. This is the header's own checksum. $ hte 01_header
00000000 b9 b3 4b 7b 01 01 03 00 02 5a 04 00 00 1e 63 03 00000010 01 02 00 00 01 13 08 00 57 48 4f 56 00 00 00 00 00000020 00 02 00 00 e0 5b 44 00 ac 62 73 88 00 5e 44 00 00000030 00 90 1c 03 8a 64 0d f0 00 ee 60 03 38 2e 02 00 00000040 80 ea c3 89 00 00 00 00 00 00 00 00 00 00 00 00 00000050 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 * 00000200
Repack firmware image, transfer to iDRAC & flash
I used TFTP to get the image file to iDRAC. Setting up a TFTP service is left as an exercise to the reader.
(I found that this is the easiest way of updating the iDRAC as I'm running FreeBSD, can't make use of Dell's bmcfwul utility, don't want to set up a boot disk or bother getting racadm running locally. YMMV.)
## Create final firmware image - should be EXACTLY the same size as the original but with different cksum $ cat 01_header 02_before_cramfs 03_cramfs_MODIFIED 04_after_cramfs > firmimg_MODIFIED.d6 ## Copy to TFTP directory, wherever that happens to be $ cp firmimg_MODIFIED.d6 /var/tftpd/firmimg.d6 ## Connect to iDRAC and update firmware -- this can be done in several ways. I used SSH access to iDRAC CLP. $ ssh email@example.com /admin1-> racadm fwupdate -g -u -a 192.168.1.1
The firmware transfer and flashing process will take a while. If you get anything other than a successful flash, issue
racadm gettracelog to find out what went wrong. It will probably be a bad checksum. Once you have successfully flashed the firmware and iDRAC has reset proceed to the next step.
Connect to root backdoor via netcat
Although it won't be a proper terminal this hack will allow you to adjust some critical things.
If for some reason netcat doesn't work, use
racadm racdump to view the iDRAC process list and determine if
nc is running. You should see something like this:
6551 root 3548 S /bin/nc -l -p 2323 -e /bin/bash
I've added empty lines below to make the exchange via netcat more readable but those wouldn't typically be there
$ netcat 192.168.1.254 2323 ## Make sure we are root whoami ==> send this root <== expect this ## Change root's password so we can su later on passwd ==> Changing password for root <== New password:calvin <===> (send "calvin") <==== Bad password: too weak <==== Retype password:calvin <===> (send "calvin") <==== Password for root changed by root <====
Before you leave netcat update a path in
/etc/passwd. Since iDRAC SSH and Telnet access turns your user into
racuser regardless of login name (and thereby grants access to the CLP shell) we change this to
/bin/sh so our user can access the system, become root and so on by issuing the following commands:
cat /flash/data0/etc/passwd | sed -e 's#/usr/bin/clpd#/bin/sh#' > /flash/data0/etc/passwd.new mv /flash/data0/etc/passwd.new /flash/data0/etc/passwd
Now break out using Ctrl-C since Ctrl-D will close the netcat process on iDRAC
Test access via iDRAC SSH or Telnet
Be aware that the root password change that we made earlier won't persist across RAC resets/firmware updates.
$ ssh firstname.lastname@example.org email@example.com's password: calvin [WPCM450 /flash/data0/home/root]$ whoami racuser [WPCM450 /flash/data0/home/root]$ su - Password: [WPCM450 ~]$ whoami root
From here you can access the original SM-CLP command line interface by issuing the command
We'll cover actual fan control in the next part.
Scripting these steps
If you find yourself having to repeat these steps multiple times you can use a simple shell script to automate a number of the steps, thereby making the whole process faster and less error prone. Here is a copy of my script but you'll probably need to make changes to reflect your environment.
Here are some other resources that might help you. They mostly pertain to older Dell PowerEdge systems and weren't completely applicable to my problem. If you aren't familiar with out-of-band systems check out OOB Management and You!
Dell PowerEdge (PE) fan woes
- Reducing Dell PE 2950/2900/2800 Fan Noise (fan mod + BMC firmware)
- How to Make a Dell PE Quieter
- Quieting the Loud Fans on a Dell PE 2950 Server
- Hacking Fan Speed on Dell PE Servers
- Quieting Dell PE 1855/1955 Blade System Fan Noise: Undocumented DRAC/MC Commands
Reverse engineering firmware
- Practical Reverse Engineering: A 5 Part Tutorial
- Reverse Engineering Linksys WAG120N
- Guessing Checksum Algorithms
- radare Reference Manual
- Netcat and Reverse Telnet