What is the CVSS score of CVE-2025-59420?

CVE-2025-59420 has a CVSS 3.1 base score of 7.5 (High). CVSS vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N. EPSS exploitation probability: 0.0%.

Which versions of Python are affected by CVE-2025-59420?

Organizations using Authlib face notable risk from CVE-2025-59420 rated CVSS 7.5. Exploitation could compromise the security of affected deployments.. A patch is available.

Is there a public PoC exploit available for CVE-2025-59420?

Yes, a public proof-of-concept exploit is available for CVE-2025-59420. Prioritise patching immediately. EPSS: 0.0%.

How to fix or mitigate CVE-2025-59420?

Within 30 days: Identify all affected systems and apply vendor patches as part of regular patch cycle. Vendor patch is available.

Python CVE-2025-59420

HIGH

Insufficient Verification of Data Authenticity (CWE-345)

2025-09-22 security-advisories@github.com

Python Privilege Escalation Authlib Red Hat

7.5

CVSS 3.1 · GitHub Advisory

Severity by source

GitHub Advisory PRIMARY

7.5 HIGH

AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N

Red Hat

7.5 HIGH

qualitative

Primary rating from GitHub Advisory.

CVSS VectorGitHub Advisory

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N

Attack Vector

Network

Attack Complexity

Low

Privileges Required

None

User Interaction

None

Scope

Unchanged

Confidentiality

None

Integrity

High

Availability

None

Lifecycle Timeline

Analysis Generated

Mar 28, 2026 - 19:13 vuln.today

Patch released

Mar 28, 2026 - 19:13 nvd

Patch available

PoC Detected

Nov 03, 2025 - 18:17 vuln.today

Public exploit code

CVE Published

Sep 22, 2025 - 18:15 nvd

HIGH 7.5

Blast Radius

ecosystem impact

† from your stack dependencies † transitive graph · vuln.today resolves 4-path depth

7 pypi packages depend on authlib (6 direct, 1 indirect)

Ecosystem-wide dependent count for version 1.6.4.

DescriptionGitHub Advisory

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.

AnalysisAI

Authlib is a Python library which builds OAuth and OpenID Connect servers. Rated high severity (CVSS 7.5), this vulnerability is remotely exploitable, no authentication required, low attack complexity. Public exploit code available.

Technical ContextAI

This vulnerability is classified under CWE-345. 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. Affected products include: Authlib. Version information: version 1.6.4.

RemediationAI

A vendor patch is available. Apply the latest security update as soon as possible. Apply vendor patches when available. Implement network segmentation and monitoring as interim mitigations.