The vulnerability lies in the handling of the JWS crit header by the gose library. While the library parses the crit field, it never checks whether the listed critical extensions are understood, contradicting RFC 7515 §4.1.11, which mandates rejecting a token that contains a crit entry for an unsupported extension. Because the library implements no header extensions, any token that contains a non‑empty crit header is treated as valid. This means an attacker can supply a JWS that carries custom or unused critical parameters and have it accepted by gose, potentially enabling the creation of forged tokens or the inclusion of malicious claims without detection. This could lead to unauthorized authentication or privilege escalation whenever the library is used to verify tokens for access control. The product affected is the Eclipse KeyPont library, specifically the GoSE implementation maintained by the Eclipse Foundation. No specific version information is provided, so all releases of the library before the correction are potentially impacted. The CVSS score for the flaw is 6.3, indicating moderate severity. The EPSS score is not available, and the vulnerability is not listed in the CISA KEV catalog. Because the flaw involves acceptance of JWS tokens sent over the network, an attacker can exploit it remotely by submitting a crafted token to any service that utilizes GoSE for token validation. The attack requires only the ability to provide a JWS with a non‑empty crit header, which is typically trivial, making the likelihood of exploitation moderate to high under a motivated threat actor.

The vulnerability resides in the Eclipse KeyPont GoSE component managed by the Eclipse Foundation. The only vendor/product reference is Eclipse KeyPont – GOSE. No affected product versions are enumerated, so any published release of this library prior to a security fix may be vulnerable.

The CVSS score of 6.3 signifies a moderate risk, but the lack of EPSS data and the absence from the KEV catalog suggest that no known exploits are actively in the wild yet. Nonetheless, because the flaw enables acceptance of JWS payloads with unsupported crit headers, an attacker who can send a token to a service using GoSE can bypass authentication checks. The attack vector is remote, depending on any network exposure of an endpoint that validates JWS tokens with GoSE.