Linux Glibc Security Fix Created a Nastier Linux Bug

A fix that was made in early June to the GNU C Library (glibc) introduced a new and nastier problem. Steven J. Vaughan-Nichols writes via ZDNet: The first problem wasn’t that bad. As Siddhesh Poyarekar, a Red Hat principal software engineer wrote, “In order to mount a minimal attack using this flaw, an attacker needs many pre-requisites to be able to even crash a program using this mq_notify bug.” Still, it needed patching and so it was fixed. Alas, the fix contained an even nastier bug. While checking the patch, Nikita Popov, a member of the CloudLinux TuxCare Team, found the problem. It turns out that it is possible to cause a situation where a segmentation fault could be triggered within the library. This can lead to any application using the library crashing. This, of course, would cause a Denial-of-Service (DoS) issue. This problem, unlike the earlier one, would be much easier to trigger. Whoops.

Red Hat gives the problem in its Common Vulnerability Scoring System (CVSS) a score of 7.5, which is “high.” An attack using it would be easy to build and requires no privileges to be made. In short, it’s bad news. Popov himself thinks “every Linux application including interpreters of other languages (python, PHP) is linked with glibc. It’s the second important thing after the kernel itself, so the impact is quite high.” […] The good news is both the vulnerability and code fix have been submitted to the glibc development team. It has already been incorporated into upstream glibc.

In addition, a new test has been submitted to glibc’s automated test suite to pick up this situation and prevent it from happening in the future. The bottom line is sometimes changed in unrelated code paths can lead to behaviors changing elsewhere without the programmer realizing what’s going on. This test will catch this situation. The Linux distributors are still working out the best way to deploy the fix. In the meantime, if you want to be extra careful — and I think you should be — you should upgrade to the newest stable version of glibc 2.34 or higher.