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CVE-2026-73683 – Authentication Bypass (Nonce Replay) – Laravel Socialite < 5.29.0

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Summary

CVE-2026-73683 is an authentication bypass vulnerability in Laravel Socialite’s Facebook provider, caused by missing nonce claim validation when processing OpenID Connect (OIDC) id_token values in the getUserByOIDCToken() function. The flaw affects all Socialite versions prior to 5.29.0 and carries a CVSS v3.1 base score of 8.1 (High). An attacker in possession of a valid, unexpired id_token issued for the same Facebook App ID can replay it against the application’s token endpoint to authenticate as the victim user without needing their credentials.

Technical details

  • Root cause: The getUserByOIDCToken() method in FacebookProvider.php validates the OIDC token’s signature, audience (aud), and issuer (iss) claims, but does not perform a session-bound comparison of the nonce claim, which is the mechanism OIDC relies on to bind a token to a specific authentication request/session.
  • Trigger conditions: An attacker must obtain a valid, unexpired id_token issued for the target application’s Facebook App ID (e.g., via network interception, token leakage, logging, referrer leakage, or a malicious app using the same client). No user interaction is required to exploit an already-captured token.
  • Attack vector: Network-based (AV:N); attack complexity is rated High (AC:H) since an attacker must first obtain a valid token issued for the correct App ID, but no privileges or user interaction are required once the token is in hand.
  • Impact: Successful exploitation allows full authentication bypass, letting an attacker impersonate the victim within the consuming application — resulting in high confidentiality, integrity, and availability impact for that user’s account/session.

Affected software

  • Laravel Socialite: all versions prior to 5.29.0 (Facebook OIDC/Limited Login provider)

Severity

  • CVSS v3.1 Base Score: 8.1 (High)
  • Vector: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H

Mitigation and recommended actions

  • Immediate: Upgrade laravel/socialite to version 5.29.0 or later, which adds nonce claim validation to the Facebook OIDC token verification flow (fixed via commit caf714f, merged in PR #789).
  • If unable to patch immediately:
    • Audit application logs and infrastructure to ensure Facebook OIDC id_token values are never exposed in URLs, logs, browser history, or referrer headers.
    • Where feasible, disable or restrict use of the Facebook Limited Login / OIDC token flow until the patch is applied.
    • Enforce short token lifetimes and monitor for anomalous authentication events (e.g., the same token or App ID used from multiple IPs/sessions in a short window).
    • After upgrading, verify that authentication flows enforce a fresh, session-bound nonce on every login attempt.

References

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