Quick answers
- Is CVE-2026-75509 exploited in the wild?
- No. Junglewise Threat Intelligence has no report of CVE-2026-75509 being exploited in the wild.
- How severe is CVE-2026-75509?
- Medium severity, with a CVSS score of 6.5, published 24 August 2026.
- Which products and versions are affected?
- Authlib Joserfc before 1.7.3.
- Is there a fix for CVE-2026-75509?
- A patch was published on 2026-07-03: Fix committed; version 1.7.3 released Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.
- How is CVE-2026-75509 attacked?
- It is attacked over the network, in a software library.
- Am I affected by CVE-2026-75509?
- Check whether you run Authlib Joserfc at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.
Technical details
The vulnerability is a logic error in JWTClaimsRegistry's claim validation. The registry applies membership matching (array containment check) to list-valued claims including iss, sub, and jti, which RFC 7519 defines as single StringOrURI values. An attacker can craft a JWT with an array-typed iss claim containing both a malicious issuer and the expected legitimate issuer; the flawed membership check accepts this as a match when an equality check was intended. The vulnerability requires the application to rely on iss validation for authentication/authorization decisions, but no special privileges or user interaction are needed. The fix (version 1.7.3) adds type validation to reject array-typed iss, sub, jti, and nonce claims.
Affected products
- authlib joserfc before 1.7.3
Timeline
- 2026-08-24: disclosed
- 2026-07-03: patched: Fix committed; version 1.7.3 released