PYSEC-2026-4358

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    PYSEC-2026-4358

    Published: 22 Oct 2026Last Modified: 30 Oct 2026

    Summary:

    Details: Authlib is a Python library which builds OAuth and OpenID Connect servers. Prior to 1.9.0, the default RFC 7523 JWTBearerGrant.get_audiences() returns an empty list, causing JWTBearerGrant.verify_claims() to require only that an aud claim exists without matching the current authorization server. An attacker holding a legitimate assertion for another service can present it to a server that shares the signing key and uses the default grant, obtaining an access token across a trust boundary. Implementations that override get_audiences() with the server's valid audience identifiers are not affected. 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-fch4-3c6x-j4gc

    Affected packages

    Package

    Name: authlib

    Purl: pkg:pypi/authlib

    Affected ranges

    Type: ECOSYSTEM

    Events:

    Introduced- 0
    Fixed -1.9.0

    Affected versions

    0.1

    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
    PYSEC-2026-4358 | CVE-DB