Vulnerabilities in OpenIDC liboauth2 software

CERT Polska has received a report about vulnerabilities in OpenIDC liboauth2 software and participated in coordination of their disclosure.

The vulnerabilityCVE-2026-54430: liboauth2 is vulnerable to Server-Side Request Forgery inoauth2_jose_jwks_aws_alb_resolve()function. The AWS ALB verifier reads bothsignerandkidfrom the unverified JWT header. Ifsignermatches the configured ARN,kidis appended toalb_base_urlwithout URL encoding or path sanitization, and the HTTP GET request is sent before signature verification. This allows an attacker to force the server to send a GET request to an attacker-chosen internal path.

The vulnerabilityCVE-2026-54431: In liboauth2 the Demonstrating Proof-of-Possession (DPoP) verifier accepts a proof whose JSON Web Key (jwk) header contains private key material. RFC 9449 section 4.3 step 7 requires the verifier to reject such a proof butoauth2_token_verify()function returns success for a malformed DPoP proof that embeds the private Elliptic Curve (EC) key in the header.

These issues were fixed in version 2.3.0

We thank Michał Majchrowicz and Marcin Wyczechowski from AFINE Team for the responsible vulnerability report.