CVE-2026-28802

CriticalPublic PoC

Published: 06 March 2026

Published

06 March 2026

Modified

09 March 2026

KEV Added

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Patch

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CVSS Score 9.8 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

EPSS Score 0.0002 4.9th percentile

Risk Priority 20 60% EPSS · 20% KEV · 20% CVSS

Summary

CVE-2026-28802 is a critical-severity Improper Verification of Cryptographic Signature (CWE-347) vulnerability in Authlib Authlib. Its CVSS base score is 9.8 (Critical).

Operationally, exploitation aligns with the MITRE ATT&CK technique Exploit Public-Facing Application (T1190); ranked at the 4.9th percentile by exploit likelihood (below the median); it is not currently listed in the CISA KEV catalog; a public proof-of-concept is referenced.

The strongest mitigations our analysis identified are NIST 800-53 RA-5 (Vulnerability Monitoring and Scanning) and SI-2 (Flaw Remediation).

Threat & Defense at a Glance

What attackers do: exploitation maps to Exploit Public-Facing Application (T1190) and 1 other technique. What defenders deploy: see the NIST 800-53 controls recommended below.

Threat & Defense Details

Mitigating Controls (NIST 800-53 r5)AI

SI-2 Flaw Remediation good match

prevent

Directly mitigates the CVE by requiring identification, prioritization, and timely patching of the Authlib library flaw in JWT signature verification.

RA-5 Vulnerability Monitoring and Scanning good match

detect

Enables proactive scanning and monitoring to identify vulnerable Authlib versions affected by the improper JWT 'alg: none' handling.

SI-10 Information Input Validation partial match

prevent

Provides defense-in-depth by validating incoming JWT inputs to reject malformed tokens with 'alg: none' or empty signatures.

MITRE ATT&CK Enterprise TechniquesAI

T1190 Exploit Public-Facing Application Initial Access

Adversaries may attempt to exploit a weakness in an Internet-facing host or system to initially access a network.

attack.mitre.org →

T1550.001 Application Access Token Lateral Movement

Adversaries may use stolen application access tokens to bypass the typical authentication process and access restricted accounts, information, or services on remote systems.

attack.mitre.org →

Why these techniques?

The JWT alg:none signature bypass directly enables remote exploitation of public-facing OAuth/OIDC apps (T1190) via forged application access tokens (T1550.001) with no privileges required.

Confidence: HIGH · MITRE ATT&CK Enterprise v18.1

NVD Description

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.

Deeper analysisAI

CVE-2026-28802 affects Authlib, a Python library used for building OAuth and OpenID Connect servers, specifically in versions from 1.6.5 up to but not including 1.6.7. The vulnerability stems from improper JWT signature verification, where tests passing a malicious JWT with the "alg: none" parameter and an empty signature unexpectedly succeeded without any application code changes, despite a failure being expected. This flaw, classified under CWE-347, carries a CVSS 3.1 base score of 9.8, reflecting its critical severity.

Remote attackers require no privileges or user interaction and can exploit this over the network with low attack complexity (AV:N/AC:L/PR:N/UI:N/S:U). By submitting such a malformed JWT to applications relying on vulnerable Authlib for token validation, attackers can bypass the signature verification step, achieving high impacts on confidentiality, integrity, and availability (C:H/I:H/A:H).

The vulnerability has been addressed in Authlib version 1.6.7. Mitigation involves upgrading to this patched version. Details on the fix are documented in the GitHub security advisory at GHSA-7wc2-qxgw-g8gg, along with relevant commits a61c2acb807496e67f32051b5f1b1d5ccf8f0a75 and b87c32ed07b8ae7f805873e1c9cafd1016761df7.