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Authlib CVE-2026-28802

HIGH
Improper Verification of Cryptographic Signature (CWE-347)
2026-03-06 security-advisories@github.com GHSA-7wc2-qxgw-g8gg
Python Authlib Information Disclosure Jwt Attack
7.7
CVSS 4.0 · Vendor: github
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Severity by source

Vendor (github) PRIMARY
7.7 HIGH
CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:H/VA:N/SC:N/SI:N/SA:N/E:P/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X
vuln.today AI
7.5 HIGH

Network-reachable, low-complexity forged token requires no privileges or interaction; impact is integrity/authentication bypass only, with no confidentiality or availability loss.

3.1 AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N
4.0 AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:H/VA:N/SC:N/SI:N/SA:N
SUSE
9.8 CRITICAL
AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
Red Hat
9.1 HIGH
qualitative

Primary rating from Vendor (github).

CVSS VectorVendor: github

CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:H/VA:N/SC:N/SI:N/SA:N/E:P/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X
Attack Vector
Network
Attack Complexity
Low
Privileges Required
None
User Interaction
None
Scope
X

Lifecycle Timeline

12
Analysis Updated
Jun 30, 2026 - 05:03 vuln.today
v5 (cvss_changed)
Analysis Updated
Jun 30, 2026 - 05:01 vuln.today
v4 (cvss_changed)
Source Code Evidence Fetched
Jun 30, 2026 - 05:00 vuln.today
Analysis Updated
Jun 30, 2026 - 05:00 vuln.today
v3 (cvss_changed)
Analysis Updated
Jun 30, 2026 - 05:00 vuln.today
v2 (cvss_changed)
Re-analysis Queued
Jun 30, 2026 - 03:24 vuln.today
cvss_changed
Severity Changed
Jun 30, 2026 - 03:24 NVD
CRITICAL HIGH
CVSS changed
Jun 30, 2026 - 03:24 NVD
9.8 (CRITICAL) 7.7 (HIGH)
Analysis Generated
Mar 12, 2026 - 22:06 vuln.today
PoC Detected
Mar 09, 2026 - 21:20 vuln.today
Public exploit code
Patch released
Mar 09, 2026 - 21:20 nvd
Patch available
CVE Published
Mar 06, 2026 - 07:16 nvd
CRITICAL 9.8

DescriptionCVE.org

Authlib is a Python library which builds OAuth and OpenID Connect servers. From version 1.6.5 to before version 1.6.7, previous tests involving passing a malicious JWT containing alg: none and an empty signature was passing the signature verification step without any changes to the application code when a failure was expected.. This issue has been patched in version 1.6.7.

AnalysisAI

Authentication bypass in Authlib (Python OAuth/OpenID Connect library) versions 1.6.5 through 1.6.6 allows remote attackers to forge JWTs by supplying a token with 'alg: none' and an empty signature, which the library accepts as valid during signature verification. Because the integrity check is silently bypassed, an attacker can craft tokens with arbitrary claims and impersonate any identity. Publicly available exploit code exists (regression-test based, via the GitHub Security Advisory), but EPSS is only 0.02% (6th percentile) and the issue is not in CISA KEV - no public exploit identified as actively used at time of analysis.

Technical ContextAI

Authlib is a widely-used Python library for building OAuth 2.0 and OpenID Connect authorization and resource servers, where JSON Web Tokens (JWT/JWS) are the core credential format. The root cause is CWE-347 (Improper Verification of Cryptographic Signature): the JWS verification path failed to reject the 'none' algorithm with an empty signature, so a token that should fail validation instead passed. The 'alg:none' attack is a classic JWT pitfall where the unsecured-JWS option defined in RFC 7515 is meant to be explicitly opt-in, but a verifier that does not enforce an algorithm allowlist treats an unsigned token as authentic. The affected CPE is cpe:2.3:a:authlib:authlib, confirming the library itself (not a specific downstream product) is the vulnerable component.

RemediationAI

Vendor-released patch: upgrade Authlib to version 1.6.7, which fixes the verification logic (commits a61c2acb807496e67f32051b5f1b1d5ccf8f0a75 and b87c32ed07b8ae7f805873e1c9cafd1016761df7). Red Hat users should apply the relevant errata for their product (e.g., RHSA-2026:6309, RHSA-2026:5665, RHSA-2026:4942 and others) via https://access.redhat.com/security/cve/CVE-2026-28802. If immediate upgrade is not possible, the most effective compensating control is to enforce an explicit algorithm allowlist in your JWT/JWS verification configuration so that 'none' is never accepted - for example, require RS256/ES256/HS256 and reject any token whose alg is 'none' or whose signature is empty; the trade-off is minimal but you must ensure every verification call site passes the allowlist, since a missed call site reopens the gap. Reference advisory: https://github.com/authlib/authlib/security/advisories/GHSA-7wc2-qxgw-g8gg.

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Vendor StatusVendor

SUSE

Severity: Critical
Product Status
SUSE Linux Enterprise Desktop 15 SP7 Fixed
SUSE Linux Enterprise High Performance Computing 15 SP7 Fixed
SUSE Linux Enterprise Module for Python 3 15 SP7 Fixed
SUSE Linux Enterprise Server 15 SP7 Fixed
SUSE Linux Enterprise Server for SAP Applications 15 SP7 Fixed

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CVE-2026-28802 vulnerability details – vuln.today
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