Vulnerability · Published Jun 18, 2026 · Assigned by GitHub_M

CVE-2026-48983pam_usb: TOCTOU race condition in pad directory creation allows symlink substitution

Medium 5.8

In plain English

A medium-severity security flaw in pam_usb from mcdope. There are no confirmed reports of exploitation so far. The chance it is exploited in the next 30 days is estimated at 0.1% (higher than 1% of all known vulnerabilities).

Severity (CVSS 3.1)5.8Medium

Exploit odds (30 days)0.1%top 98.9% of all CVEs

Exploited in the wildNo reportsCISA SSVC: none

Attack toolingNoneno public tooling known

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.

Affected products (as reported)

Vendor	Product	Versions
mcdope	pam_usb	< 0.9.2

Weakness: CWE-367 · Vector: CVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:L/A:L

References

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