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CVE-2026-76214 – Authentication Bypass via WebAuthn Replay – phpMyFAQ before 4.1.7

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Summary

CVE-2026-76214 is a critical authentication bypass vulnerability in phpMyFAQ, an open-source FAQ management application, caused by improper handling of WebAuthn login challenges. Because the application never persists the per-login WebAuthn challenge to the database, an attacker who captures a single successful WebAuthn login assertion can replay it indefinitely to authenticate as the victim, without possessing the victim’s hardware security key. The issue affects all phpMyFAQ versions prior to 4.1.7 and carries a CVSS v4.0 base score of 9.1 (Critical).

Technical details

  • Root cause: The prepareForLogin function generates a per-login WebAuthn challenge and stamps it onto the user’s key object in memory, but neither of the WebAuthn login controllers calls the method needed to save the updated key back to the database.
  • Trigger condition: Because the challenge is never persisted, keys re-read from storage during authentication lack a challenge value, and the anti-replay comparison is bypassed by its own null-value guard (intended as a fail-safe, it instead fails open).
  • Attack vector: Network-based; an attacker who obtains a valid WebAuthn assertion (e.g., via network interception, logging, or a proxy) can resend the exact same login request repeatedly and be authenticated each time.
  • Impact: Full authentication bypass — an attacker can log in as the targeted user indefinitely without needing the physical hardware authenticator or any further user interaction, undermining the core replay-protection guarantee of WebAuthn.

Affected software

  • phpMyFAQ versions prior to 4.1.7 (all versions through 4.1.5)
  • Fixed in phpMyFAQ 4.1.7

Severity

  • CVSS v4.0: 9.1 (Critical) — CVSS:4.0/AV:N/AC:H/AT:P/PR:N/UI:N/VC:H/VI:H/VA:N/SC:N/SI:N/SA:N
  • CVSS v3.1: 7.4 (High) — CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:N
  • CWE-294: Authentication Bypass by Capture-replay

Mitigation and recommended actions

  • Immediate: Upgrade phpMyFAQ to version 4.1.7 or later, which persists WebAuthn challenge state correctly and closes the replay window.
  • If patching is not immediately possible: Disable WebAuthn as a login method until the upgrade can be applied, monitor authentication logs for repeated identical login requests, and ensure sessions are terminated/rotated regularly to limit the impact of any replayed assertion.

How IONIX identifies potentially affected assets

IONIX matches the following signals against data already collected when it crawled the asset; identifying the technology sends no request beyond that crawl.

  • Named response header (Set-Cookie): pmf_sid=
  • Meta tag content (application-name): phpMyFAQ followed by a version number
  • Raw response body: by phpMyFAQ followed by a version number

References

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