PYSEC-2026-4355

    Dashboard / Vulnerabilities / PYSEC-2026-4355

    PYSEC-2026-4355

    Published: 22 Oct 2026Last Modified: 30 Oct 2026

    Summary:

    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: https://github.com/authlib/authlib/releases/tag/v1.9.0, https://github.com/authlib/authlib/commit/e3bd41cb29dcfee434453b135ffb487884baeedf, https://github.com/authlib/authlib/pull/945, https://github.com/authlib/authlib/security/advisories/GHSA-7vr2-2fgp-9w7p

    Affected packages

    Package

    Name: authlib

    Purl: pkg:pypi/authlib

    Affected ranges

    Type: ECOSYSTEM

    Events:

    Introduced- 1.3.1
    Fixed -1.9.0

    Affected versions

    1.3.1
    1.3.2

    Common Vulnerability Scoring System

    Attack Vector
    Network
    Adjacent
    Local
    Physical
    Privileges Required
    None
    Low
    High
    User Interaction
    None
    Required
    Scope
    Unchanged
    Changed
    Confidentiality
    None
    Low
    High
    Integrity
    None
    Low
    High
    Availability
    None
    Low
    High