CVE-2026-48983 pam_usb: TOCTOU race condition in pad directory creation allows symlink substitution
A local attacker can exploit a race condition in pam_usb to substitute symlinks, potentially exposing one-time pad values or disrupting authentication.
- Exploited in the wild
- Not known
- Login needed
- Any signed-in user
- Attackable
- Local or same network only
- Victim action needed
- Not needed
- Fix
- None listed
What is CVE-2026-48983?
CVE-2026-48983 is a medium-severity vulnerability in mcdope pam_usb, published on 18 Jun 2026. It can only be exploited from the same machine or local network, with no action from the victim.
Official 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.
Weakness: CWE-367
Which versions are affected by CVE-2026-48983?
How do I fix CVE-2026-48983?
No fix has been published for CVE-2026-48983 yet. Limit exposure of the affected software until one is available.
Is CVE-2026-48983 being exploited?
There is no known exploitation of CVE-2026-48983 in the wild and no public exploit code.
Sources
Also known as GHSA-4j8q-67fq-3xc3.