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CVE-2026-87004 – OIDC Authentication Bypass via Unverified ID Tokens – Tugtainer ≤ 1.31.2

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Summary

CVE-2026-87004 is an authentication bypass vulnerability in Tugtainer, a self-hosted application for automating Docker container updates. The flaw lies in Tugtainer’s OpenID Connect (OIDC) login flow, where the identity provider’s id_token is decoded without verifying its signature, issuer, audience, or expiration, allowing an attacker to forge a token that grants them a valid, authenticated session. The issue carries a CVSS v3.1 score of 8.1 (High) and affects all Tugtainer versions prior to 1.31.3.

Technical details

  • Root cause: The OIDC provider module (backend/modules/auth/providers/auth_oidc_provider.py) decodes the id_token returned by the identity provider’s token endpoint using jose.jwt.get_unverified_claims() instead of a verifying call such as jwt.decode().
  • Trigger conditions: This skips cryptographic signature verification, issuer (iss) validation, audience (aud) validation, and expiration (exp) checking entirely during the OIDC login flow.
  • Attack vector: Network-exploitable (AV:N) with high attack complexity (AC:H), requiring no privileges (PR:N) and no user interaction (UI:N). An attacker able to present a crafted/unverified id_token to Tugtainer’s OIDC callback can have it accepted as valid.
  • Impact: Claims extracted from the unverified token (email, sub, preferred_username) are used directly as the session identifier (user_id), enabling an attacker to assume the identity of any user, including administrators, resulting in full compromise of confidentiality, integrity, and availability of the Tugtainer instance and the Docker environment it manages.

Affected software

  • Quenary Tugtainer — all versions prior to 1.31.3

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 Tugtainer to version 1.31.3 or later, which replaces the unverified claims extraction with proper signed/validated JWT decoding.
  • If immediate patching is not possible: Disable OIDC-based login on internet-exposed Tugtainer instances until patched, and restrict network access to the Tugtainer web interface to trusted hosts/VPN only. Review authentication logs for unexpected logins via OIDC, particularly sessions tied to unfamiliar email/sub/preferred_username values.

References

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