An unpatched critical vulnerability impacting a wireless video bridge used by DirecTV allows for an attacker to remotely execute code on the vulnerable devices, Zero-Day Initiative researchers reveal.
The security vulnerability was discovered in the Linksys WVBR0-25 wireless video bridge, which was designed to pair with the Wireless Genie Mini (C41W) cable box to ensure communication with DirecTV’s main Genie DVR.
Tracked as CVE-2017-17411 and featuring a CVSS score of 10, the vulnerability was discovered by Trend Micro DVLabs researcher Ricky Lawshae, who says that authentication isn’t necessary when attempting to exploit the vulnerability for executing arbitrary code.
“The specific flaw exists within the web management portal. The issue lies in the lack of proper validation of user data before executing a system call. An attacker could leverage this vulnerability to execute code with root privileges,” a ZDI advisory reads.
While attempting to browse to the web server on the device, Lawshae discovered that, instead of a login prompt or an index page, the service would deliver “the output of several diagnostic scripts containing just about everything you could want to know about the bridge, including the WPS pin, connected clients, running processes, and much more.”
Not only is this an information disclosure issue, but the log file also revealed the commands being executed and the output of every command. Moreover, it showed that the user’s IP address and user-agent were used in a system command as a form of access logging or tracking functionality.
Nonetheless, the device isn’t properly sanitizing the user-agent it is given and the researcher was able to change the user-agent and send untrusted data to the system for execution. What Lawshae discovered was that the system executed the command as root, without a login prompt or input sanitization before sending the command to the function responsible for its execution.
Because the lighttpd process runs with root privileges, executed commands run with root privileges as well, even if they come from untrusted input.
“It literally took 30 seconds of looking at this device to find and verify an unauthenticated remote root command injection vulnerability,” Lawshae says.
After performing a deeper analysis of the device, the researcher discovered that it was running a lighttpd web server. It was configured to render a SysInfo.asp file when browsing to the root of the website, and this file was the page displaying all the diagnostic output.
“It also showed dispatcher.cgi was actually a symbolic link to apply.cgi, which itself is a compiled ARC executable file used as kind of a “do everything” agent for the web server. It was in apply.cgi that I found the actual root cause,” Lawshae, who also published a video detailing the vulnerability, explains.
The ZDI attempted to work with Linksys to address the vulnerability, but to no avail. Although it was informed on the bug in June, the company hasn’t even acknowledged it yet, which determined ZDI to publish the 0-day report.
SecurityWeek contacted Linksys for a comment on the matter but hasn’t received a response yet. We’ll update the article as soon as we hear back from them.
“In the absence of an actual patch from the vendor, users should protect themselves by limiting the devices that can interact with the WVBR0-25 to those that actually need to reach it,” Lawshae concludes.
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