Use Linux? Stop what you’re doing and apply this patch

A buffer-overflow vulnerability uncovered Tuesday in the GNU C Library poses a serious threat to countless Linux users.

Dating back to the release of glibc 2.9 in 2008, CVE-2015-7547 is a stack-based buffer overflow bug in the glibc DNS client-side resolver that opens the door to remote code execution when a particular library function is used. Software using the function can be exploited with attacker-controlled domain names, attacker-controlled DNS servers or man-in-the-middle attacks.

Glibc, which was also at the core of the “Ghost” vulnerability found last year, is a C library that defines system calls and other basic functions on Linux systems. Its maintainers had apparently been alerted of the new problem last July, but it’s not clear if any remediation effort was launched at that time.

Google and Red Hat independently reported the problem this week and a patch is now available.

“Our initial investigations showed that the issue affected all the versions of glibc since 2.9,” Google explained in its Online Security Blog. “You should definitely update if you are on an older version, though. If the vulnerability is detected, machine owners may wish to take steps to mitigate the risk of an attack.”

For those unable to patch immediately, Google has found some mitigations that may help prevent exploitation, including limiting response sizes accepted by the DNS resolver locally.

The company does not plan to release its exploit code, but it did release proof-of-concept code to help users determine if they’re affected by the issue and verify any mitigations.

“The part that makes this interesting is that DNS is a core infrastructure component, which means that a lot of subsystems and applications could potentially be impacted,” said Mark Loveless, a senior security researcher at Duo Security. “The main things listed initially were ssh, curl, wget and similar command-line Linux utilities, but it is possible that other processes could also use the library calls in the exact way needed for exploit.”

In theory, other non-Windows systems that use glibc could be affected as well, Loveless added, including other Unix-based operating systems or even operating systems for mobile devices or tablets.

All Linux servers and Web frameworks such as Rails, PHP and Python are likely affected, as are Android apps running glibc, according to a post by Kaspersky Lab.