CVE-2025-59420
unknown
CVSS v3
—
CVSS v2
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VIR risk
—
Description
Authlib is a Python library which builds OAuth and OpenID Connect servers. Prior to version 1.6.4, Authlib’s JWS verification accepts tokens that declare unknown critical header parameters (crit), violating RFC 7515 “must‑understand” semantics. An attacker can craft a signed token with a critical header (for example, bork or cnf) that strict verifiers reject but Authlib accepts. In mixed‑language fleets, this enables split‑brain verification and can lead to policy bypass, replay, or privilege escalation. This issue has been patched in version 1.6.4.
Predictions
Exploit likelihood
30%
Patch ETA
—
Heuristic predictions, AS-IS, for prioritization only.
Mitigations
Vendor advisory: debian — https://security-tracker.debian.org/tracker/CVE-2025-59420
OS impact
| OS | Version | Status | Fixed in |
|---|---|---|---|
| debian | bookworm | fixed | 1.2.0-1+deb12u1 |
| debian | bullseye | fixed | 0.15.4-1+deb11u1 |
| debian | forky | fixed | 1.6.4-1 |
| debian | sid | fixed | 1.6.4-1 |
| debian | trixie | fixed | 1.6.0-1+deb13u1 |
Package impact
| Ecosystem | Package | Vulnerable | Fixed |
|---|---|---|---|
| PyPI | authlib | <1.6.4 | 1.6.4 |
References
- https://github.com/authlib/authlib/security/advisories/GHSA-9ggr-2464-2j32
- https://nvd.nist.gov/vuln/detail/CVE-2025-59420
- https://github.com/authlib/authlib/commit/6b1813e4392eb7c168c276099ff7783b176479df
- https://github.com/authlib/authlib
- https://lists.debian.org/debian-lts-announce/2025/10/msg00032.html
- https://security-tracker.debian.org/tracker/CVE-2025-59420
Verify integrity in audit chain (admin only). AS-IS.