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.

The remote Ubuntu 22.04 LTS / 24.04 LTS host has a package installed that is affected by multiple vulnerabilities as referenced in the USN-8065-1 advisory.

    Millie Solem discovered that Authlib did not properly restrict algorithm selection during JWT     verification, allowing HMAC verification with asymmetric public keys when no algorithm was specified. A     remote attacker could possibly use this issue to bypass signature verification and forge tokens, resulting     in authentication bypass or privilege escalation. (CVE-2024-37568)

    Muhammad Noman Ilyas discovered that Authlib did not properly enforce critical header parameter handling     during JSON Web Signature verification, leading to unknown critical parameters being incorrectly accepted.
    A remote attacker could possibly use this issue to bypass security policies in mixed deployments,     resulting in authentication bypass, replay attacks, or privilege escalation. (CVE-2025-59420)

    Muhammad Noman Ilyas discovered that Authlib did not properly limit the size of JSON Web Signature or JSON     Web Token header and signature segments. A remote attacker could possibly use this issue to cause     excessive memory or processor consumption, leading to a denial of service. (CVE-2025-61920)

    Muhammad Noman Ilyas discovered that Authlib performed unbounded decompression when processing certain     compressed encrypted tokens. A remote attacker could possibly use this issue to send a specially crafted     token that can be expanded to a large size during decompression, causing a denial of service.
    (CVE-2025-62706)

    It was discovered that Authlib did not properly bind cached state information to the initiating user     session during OAuth authentication flows. A remote attacker could possibly use this issue to perform     cross- site request forgery attacks, resulting in unauthorized actions or authentication bypass. This     issue only affected Ubuntu 24.04 LTS. (CVE-2025-68158)

Tenable has extracted the preceding description block directly from the Ubuntu security advisory.

Note that Nessus has not tested for these issues but has instead relied only on the application's self-reported version number.

The remote Debian 11 host has packages installed that are affected by multiple vulnerabilities as referenced in the dla-4352 advisory.

    -------------------------------------------------------------------------     Debian LTS Advisory DLA-4352-1                debian-lts@lists.debian.org     https://www.debian.org/lts/security/                       Daniel Leidert     October 29, 2025                              https://wiki.debian.org/LTS
    -------------------------------------------------------------------------

    Package        : python-authlib     Version        : 0.15.4-1+deb11u1     CVE ID         : CVE-2024-37568 CVE-2025-59420 CVE-2025-61920 CVE-2025-62706


    Multiple vulnerabilities have been found in python-authlib, a Python     library for OAuth and OpenID Connect servers.

    CVE-2024-37568

        Unless an algorithm is specified in a jwt.decode call, HMAC verification         is allowed with any asymmetric public key.

    CVE-2025-59420

        Authlibs JWS verification accepts tokens that declare unknown critical         header parameters (crit), violating RFC 7515 mustunderstand semantics.
        An attacker can craft a signed token with a critical header that strict         verifiers reject but Authlib accepts. In mixedlanguage fleets, this         enables splitbrain verification and can lead to policy bypass, replay,         or privilege escalation.

    CVE-2025-61920

        Authlibs JOSE implementation accepts unbounded JWS/JWT header and         signature segments which can lead to a DoS during verification.

    CVE-2025-62706

        Authlibs JWE zip=DEF path performs unbounded DEFLATE decompression         which can lead to a DoS.


    For Debian 11 bullseye, these problems have been fixed in version     0.15.4-1+deb11u1.

    We recommend that you upgrade your python-authlib packages.

    For the detailed security status of python-authlib please refer to     its security tracker page at:
    https://security-tracker.debian.org/tracker/python-authlib

    Further information about Debian LTS security advisories, how to apply     these updates to your system and frequently asked questions can be     found at: https://wiki.debian.org/LTS     Attachment:
    signature.asc     Description: This is a digitally signed message part

Tenable has extracted the preceding description block directly from the Debian security advisory.

Note that Nessus has not tested for these issues but has instead relied only on the application's self-reported version number.

The Linux/Unix host has one or more packages installed that are impacted by a vulnerability without a vendor supplied patch available.

  - 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 mustunderstand 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 mixedlanguage     fleets, this enables splitbrain verification and can lead to policy bypass, replay, or privilege     escalation. This issue has been patched in version 1.6.4. (CVE-2025-59420)

Note that Nessus relies on the presence of the package as reported by the vendor.

ID	Name	Product	Family	Severity
300274	Ubuntu 22.04 LTS / 24.04 LTS : Authlib vulnerabilities (USN-8065-1)	Nessus	Ubuntu Local Security Checks	high
271941	Debian dla-4352 : python-authlib-doc - security update	Nessus	Debian Local Security Checks	high
265880	Linux Distros Unpatched Vulnerability : CVE-2025-59420	Nessus	Misc.	high

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