CVE-2026-77130 in SYSSY Extension
Summary
by MITRE • 08/25/2026
The extension fails to properly validate the expiration of a client-supplied JWT token, allowing an attacker in control of a valid API key to authenticate with an expired token. Exploitation requires the attacker to already be in control of the SYSSY project's API key.
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Analysis
by VulDB Data Team • 08/25/2026
This vulnerability represents a critical authentication bypass within a software extension that relies on JSON Web Tokens for identity verification and access control. The core technical flaw lies in the failure of the application logic to enforce temporal constraints associated with the JWT structure, specifically ignoring or incorrectly parsing the expiration claim typically denoted as exp. In standard OAuth 2.0 and OIDC implementations, tokens are issued with a finite lifespan to limit the window of opportunity for attackers who might compromise credentials. By neglecting to validate that the current system time is less than the value stored in the token's expiration field, the extension treats an expired credential as valid indefinitely. This oversight effectively nullifies one of the primary security mechanisms designed to mitigate the impact of stolen or leaked tokens, allowing sessions to persist long after they should have been terminated by the identity provider.
The operational impact of this flaw is significant for any system relying on this extension for secure API communication. An attacker who has obtained a valid API key can leverage it to generate or obtain JWTs that are technically expired but still accepted by the vulnerable component. This allows the attacker to maintain persistent access to protected resources without needing to rotate credentials immediately, as they can reuse old tokens indefinitely. Furthermore, this flaw complicates incident response and forensic analysis because traditional log monitoring for token expiration events may not trigger alerts if the extension silently accepts these invalid assertions. The security posture is further degraded because it undermines the principle of least privilege over time; a key that should have been revoked or refreshed remains functional in an unauthorized context, potentially leading to data exfiltration, unauthorized configuration changes, or lateral movement within the target environment depending on the permissions associated with that API key.
From a classification perspective, this issue aligns directly with CWE-287 Improper Authentication and CWE-613 Insufficient Session Expiration. The failure to verify temporal validity is a specific subtype of improper authentication where the system fails to correctly enforce established security policies regarding session lifetime. In terms of adversary behavior as defined by MITRE ATT&CK, this vulnerability facilitates T1078 Valid Accounts, specifically allowing an attacker to maintain access using compromised credentials that would otherwise be invalidated. It also relates to T1528 Steal Application Access Token if the initial compromise involved token theft, although the primary exploit here is the misuse of a stolen API key combined with poor validation logic. The lack of proper timestamp verification means that even if an attacker does not actively forge tokens but simply replays old ones captured from network traffic or logs, they can successfully authenticate to the service.
Mitigation strategies must focus on enforcing strict temporal validation within the authentication middleware or library used by the extension. Developers should ensure that every JWT processed includes a check against the current system time using a secure clock source to prevent skew-related issues while still rejecting tokens where now is greater than exp. It is also advisable to implement short-lived access tokens paired with refresh tokens, ensuring that even if an access token is compromised and expired logic fails, its utility window remains narrow. Additionally, implementing certificate-based mutual TLS or additional signature verification steps can provide defense in depth. Organizations should immediately rotate the affected API keys as a precautionary measure while patches are developed, since no amount of client-side validation can fully compensate for server-side trust failures. Regular security audits and static code analysis focused on authentication flows will help identify similar oversights before they reach production environments.