CVE-2026-87004 in Tugtainer
Summary
by MITRE • 09/30/2026
Tugtainer is a self-hosted app for automating updates of Docker containers. Prior to version 1.31.3, when the OIDC login flow completes, 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 jwt.decode(). This skips signature verification, audience (aud) validation, issuer (iss) validation, and expiry (exp) checking entirely. The extracted claims (email/sub/preferred_username) are then used directly as the user_id for the resulting Tugtainer session. This issue has been patched in version 1.31.3.
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Analysis
by VulDB Data Team • 09/30/2026
The vulnerability identified in Tugtainer prior to version 1.31.3 represents a critical authentication bypass rooted in improper validation of JSON Web Tokens during the OpenID Connect login flow. When an user initiates the OIDC process, the application receives an id_token from the identity provider's token endpoint. Instead of utilizing standard cryptographic verification methods, the backend module auth_oidc_provider.py employs jose.jwt.get_unverified_claims() to extract data from this token. This function is designed solely for reading payload contents without performing any security checks, effectively treating a potentially malicious or forged token as trustworthy source material for session creation.
The core technical flaw lies in the complete omission of signature verification and standard claim validation steps that are mandatory for secure OIDC implementations. By skipping these checks, the application fails to verify the issuer (iss) field, allowing tokens issued by unauthorized identity providers to be accepted. It also neglects audience (aud) validation, meaning a token intended for a different service could be used to access Tugtainer. Furthermore, expiry (exp) checking is bypassed, permitting expired or future-dated tokens to authenticate users successfully. Most critically, the absence of signature verification means that an attacker can craft arbitrary JWTs with any desired claims without possessing the private key associated with the identity provider's signing certificate.
The operational impact of this vulnerability is severe, as it allows for complete authentication bypass and unauthorized access. Since the extracted claims such as email or preferred_username are directly mapped to the user_id field in Tugtainer sessions, an attacker can forge a token specifying any username they wish to impersonate. This capability enables privilege escalation if the forged identity corresponds to an administrative account, or it allows for session hijacking and data exfiltration by assuming the identity of legitimate users. The lack of integrity protection on the authentication flow undermines the fundamental trust model of the OIDC protocol, rendering all user accounts vulnerable to takeover regardless of their actual password strength or multi-factor authentication status if such features are tied to the initial login event.
This vulnerability aligns with CWE-287 Improper Authentication and CWE-345 Insufficient Verification of Data Authenticity from the Common Weakness Enumeration standards. In terms of offensive security tactics, it corresponds to ATT&CK technique T1621 Multi-Factor Request Interception or more broadly T1078 Valid Accounts when considering the abuse of forged credentials to gain legitimate-looking access. The failure to validate token signatures and claims is a classic example of trusting unverified input in authentication contexts, which can lead to full system compromise depending on the application's role within an organization.
To mitigate this risk, organizations running Tugtainer must immediately upgrade to version 1.31.3 or later where the code has been patched to use jwt.decode() with appropriate verification options enabled. This ensures that signature validation is performed using the correct public keys obtained from the identity provider's discovery endpoint. Additionally, developers should ensure that audience and issuer claims are strictly validated against expected values for their specific deployment environment. For systems already exposed before patching, it is advisable to review access logs for anomalous login patterns or tokens with unusual claim structures and rotate all user credentials as a precautionary measure until the update is applied.