Description

pam_usb provides hardware authentication for Linux using ordinary removable media. In versions prior to 0.9.2, a symlink race condition exists in per-device and per-user pad directory creation. pam_usb uses a check-then-act pattern: it calls lstat() to test for existence and then calls mkdir() separately to create the directory. A local attacker can win the race between these calls by replacing the target path with a symlink to a directory they control. If successful, one-time pad files may be written to an attacker-controlled location, potentially exposing future pad values before use or disrupting authentication. This issue has been fixed in version 0.9.2.

Weaknesses 1

References 2

• github.com https://github.com/mcdope/pam_usb/releases/tag/0.9.2
• github.com https://github.com/mcdope/pam_usb/security/advisories/GHSA-4j8q-67fq-3xc3

Remediation