Executive brief
Erlef oidcc is a library used to implement OpenID Connect authentication in Erlang applications. A flaw in signature verification allows attackers without the identity provider's signing key to forge authentication tokens by encrypting unsigned claims, enabling account impersonation and unauthorized access to any user account.
Technical details
This is an improper cryptographic signature verification vulnerability (CWE-347) in the JWT validation logic. The vulnerability exists in oidcc_jwt_util:verify_decrypted_token/4 and oidcc_token:int_validate_jwt/4, where decrypted JWE payloads that are not signed JWS are accepted as valid without verifying a signature. According to OpenID Connect Core 1.0, an encrypted ID token must be signed then encrypted (Nested JWT), but oidcc accepted unsigned plaintext claims as fully validated. The JARM path is reachable through the browser front channel, allowing unauthenticated network-based exploitation. An attacker with access to the relying party's public encryption key can mint tokens with arbitrary subject, issuer, and audience claims. This affects versions 3.2.0-beta.1 through 3.8.x; version 3.9.0 and later contain the fix.
Affected products
- Erlef oidcc 3.2.0-beta.1 to 3.8.x
Timeline
- 2026-08-30: disclosed: CVE-2026-75759 published