Authlib CVE-2026-96760

Exploitation requires that the target application process incoming tokens through Authlib's JsonWebSignature.deserialize_json() (the JWS JSON Serialization code path) and trust the returned payload for an authentication, authorization, or integrity decision, on Authlib version 1.7.2 or earlier. Under CVSS AV:N/AC:L/PR:N/UI:N there is no authentication, user interaction, or special attacker configuration needed; however, the practical limiting factor is application-side usage - apps that only use compact JWS serialization, independently enforce keys/signatures, or do not use this method for security decisions are not exposed. No non-default server configuration is otherwise required.

This is a genuine high-severity flaw, not merely a high-CVSS paper tiger. The CVSS 3.1 vector (AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H, 9.8) describes remote, unauthenticated, low-complexity exploitation, which is consistent with a signature-verification bypass in a widely-used Python security library: any application that verifies JWS tokens via JsonWebSignature.deserialize_json() would accept forged, unsigned payloads as authentic. SSVC reinforces concern - Technical Impact is 'total' and the flaw is 'Automatable: yes' (forging/replaying a JSON-serialized JWS is trivially scriptable) - but SSVC Exploitation is 'none', EPSS is only 0.12% (2nd percentile), there is no CISA KEV listing, and no public exploit is identified, indicating no observed exploitation yet. The signals therefore diverge: raw CVSS/SSVC impact are severe, while exploitation-probability signals are low - a classic 'high impact, not-yet-exploited' profile where the real-world risk is strongly conditioned on whether a given application actually uses the vulnerable deserialize_json() JSON-serialization path for security decisions. The description's 'C:H/I:H/A:H' is somewhat generous for a signature bypass (the core impact is forged/trusted content, i.e. integrity and consequent confidentiality/impersonation; availability impact is not described) - treat A:H as inherited from the library's worst-case use rather than an intrinsic property.

An application uses Authlib (<=1.7.2) to authenticate or authorize requests by calling JsonWebSignature.deserialize_json() on an incoming JSON-serialized JWS and trusting the returned payload. An unauthenticated remote attacker crafts a JWS JSON object with an arbitrary payload and no valid signature; deserialize_json() returns it as 'verified' without any cryptographic key check, letting the attacker forge identity claims or integrity-protected data to bypass authentication. No public exploit is identified at time of analysis, though the technique is trivial and 'Automatable: yes' per SSVC.