OIDC Library CVE-2020-16759: Encrypted Unsigned ID Token Accepted, Allowing Identity Spoofing

Vulnerability Summary: Encrypted but Unsigned ID Token Accepted Without Signature Verification Vulnerability Overview Vulnerability Name: Encrypted Unsigned ID Token Accepted Without Signature Verification Severity: High (7.6 / 10) CVE ID: CVE-2020-16759 Core Issue: The library treats encrypted but unsigned ID Tokens as if they were signed JWS and attempts signature verification. When verification fails and an exception is thrown, the error is silently swallowed, and the claims are parsed and returned as a success, allowing an attacker to forge arbitrary identity claims. Scope of Impact Affected Package: (Erlang) Affected Versions: >= 3.2.0-beta.1 and < 3.9.0 Fixed Version: 3.9.0 Impact: An unauthenticated attacker can forge arbitrary identity claims and impersonate any user to access relying party pages without leaking the service provider's signing key or the relying party's key, enabling account takeover. Fix Details Upgrade to 3.9.0 or later. Fix Method: Implement signature verification for encrypted ID Tokens and reject unsigned encrypted Tokens. PoC (Exploitation Steps) 1. Obtain the relying party's public key JWK and encrypt the ID Token response targeting its claims. 2. Construct a claims set containing the real user and client ID; use arbitrary values for fields such as , , , and , or configure it so that the relying party rejects the token. 3. During serialization, do not sign the token, then encrypt it using the relying party's public key. 4. Submit it as an ID Token or JARM response; the claims will be returned as-is. Key Code/References Introducing Commit: Patch Commit: Related Documentation: - OpenID Connect Core 1.0, section 2.0 (ID Token) - JARM response encoding and processing rules

Goal Reached Thanks to every supporter — we hit 100%!

OIDC Library CVE-2020-16759: Encrypted Unsigned ID Token Accepted, Allowing Identity Spoofing

More from this source