PYSEC-2026-4355
See a problem?- Import Source
- https://github.com/pypa/advisory-database/blob/main/vulns/authlib/PYSEC-2026-4355.yaml
- JSON Data
- https://api.osv.dev/v1/vulns/PYSEC-2026-4355
- Aliases
- Published
- 2026-10-22T22:18:04Z
- Modified
- 2026-10-30T10:00:02Z
- Severity
-
- 9.1 (Critical) CVSS_V3 - CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N CVSS Calculator
- Summary
- [none]
- Details
-
Authlib is a Python library which builds OAuth and OpenID Connect servers. From 1.3.1 until 1.9.0, OctKey.import_key() checks asymmetric-key markers only at byte zero while Authlib's PEM loaders accept leading whitespace, comments, or a byte-order mark. In deployments that use the documented mixed algorithm registry and already configure verification with PEM or certificate bytes containing such a prefix, an unauthenticated attacker who knows those same public-key bytes can use them as an HMAC secret and forge HS256 tokens with arbitrary identity or authorization claims. This is a bypass of the remediation for CVE-2024-37568. The module-level jwt object reaches OctKey.import_key() in authlib/jose/rfc7518/oct_key.py, where POSSIBLE_UNSAFE_KEYS fails to identify prefixed asymmetric key material. This issue is fixed in version 1.9.0.
- References
Affected packages
PyPI / authlib
Package
- Name
- authlib
- View open source insights on deps.dev
- Purl
- pkg:pypi/authlib