CVE-2026-114615

What it actually does

Authlib's OctKey.import_key() only checks for asymmetric key markers at byte zero, allowing prefixed PEM or certificate data (whitespace, comments, BOM) accepted by PEM loaders to be treated as an HMAC secret. This enables unauthenticated forgery of HS256-signed JWTs with arbitrary claims when the mixed algorithm registry is used.

Why it matters to the business

Attackers can impersonate any user or escalate privileges by forging valid tokens, leading to unauthorized access to protected resources and potential data breaches in OAuth/OIDC deployments relying on this library.

How an attack unfolds

An attacker obtains the public key bytes used for verification, crafts an HS256 JWT using those bytes as the HMAC secret with chosen claims, and submits it to an endpoint that accepts the mixed registry. The flawed import logic treats the prefixed asymmetric material as a symmetric key, bypassing signature checks.

How to fix it

Upgrade Authlib to version 1.9.0 or later. Ensure all verification uses the strict algorithm registry without mixing symmetric and asymmetric keys. Validate that PEM loaders reject unexpected prefixes during key import.

How to confirm the fix worked

Confirm library version is 1.9.0+. Test key import with prefixed PEM data to ensure asymmetric markers are still detected. Audit JWT verification code for use of the documented mixed algorithm registry.

Typical attack path

1. Obtain the public key bytes or certificate configured for verification
2. Construct a JWT header specifying HS256 and arbitrary claims
3. Sign the token using the public key bytes as HMAC secret
4. Submit the forged token to an authenticated endpoint
5. Bypass authorization due to accepted signature

How to detect it

Inspect application logs for JWTs accepted with HS256 when asymmetric keys are configured. Search for token validation events using public key material as an HMAC secret. Review authentication flows for sudden privilege changes without corresponding user activity.

What your security team should do

• Immediately upgrade all Authlib installations to 1.9.0
• Review and restrict JWT algorithm registries to prevent HS256 with asymmetric keys
• Monitor for unexpected JWT signature successes with known public keys
• Rotate any exposed verification keys if exploitation is suspected