🚨 CRITICAL: CVE-2026-27962 - Authlib JWS Signature Verification Bypass

[jjasghar]

🚨 CRITICAL: CVE-2026-27962 - Authlib JWS Signature Verification Bypass

Severity: CRITICAL

GHSA: GHSA-wvwj-cvrp-7pv5
CVE: CVE-2026-27962
Affected Package: authlib
Impact: Cryptographic Signature Bypass

Description

Critical vulnerability in Authlib enabling JWS (JSON Web Signature) signature verification bypass through JWK (JSON Web Key) header injection. This allows attackers to forge valid signatures and compromise authentication/integrity guarantees.

Impact Details

• Signature Verification Bypass: Attackers can create forged tokens that appear valid
• JWK Header Injection: Malicious JWK headers can override key validation logic
• Authentication & Integrity Attacks: Compromises trust in signed assertions/tokens
• Affected Files: 18 files in the repository

Security Implications

1. Forged authentication tokens accepted as legitimate
2. Introspection of protected resources without proper authorization
3. Potential privilege escalation through token manipulation
4. Breach of non-repudiation guarantees

Remediation Steps

1. Update authlib package to patched version per GHSA-wvwj-cvrp-7pv5
2. Review all JWT/JWS validation logic for header injection vulnerabilities
3. Implement strict JWK header validation and key pinning where appropriate
4. Audit token issuance and verification flows across the codebase

References

• GHSA-wvwj-cvrp-7pv5
• CVE-2026-27962

Priority

IMMEDIATE ACTION REQUIRED - Cryptographic bypass vulnerabilities undermine fundamental security guarantees.

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Automated security scan detected this critical vulnerability. Please prioritize remediation.