What’s Vulnerable › Vulnerabilities

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

• Severity: medium (CVSS 5.8 v3.1)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 0.1% probability of exploitation in the next 30 days
• Public exploit or detection template: none known
• Published: 2026-06-18 · updated 2026-10-26
• Weakness: CWE-367

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

• mcdope pam_usb: before 0.9.2

References

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

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