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.