CVE-2026-75759

oidcc, the Erlang Ecosystem Foundation's OpenID Connect client library for Erlang/Elixir, versions 3.2.0-beta.1 up to (but not including) 3.9.0 accept encrypted ID tokens and JARM responses that carry no nested JWS signature and treat them as fully validated, contrary to OpenID Connect Core 1.0 section 2 and JARM processing rule 5. An unauthenticated attacker who knows the relying party's public encryption key can submit a JWE wrapping arbitrary claims with any subject, issuer, and audience, and the code in oidcc_jwt_util:verify_decrypted_token/4 and oidcc_token:int_validate_jwt/4 accepts it as verified without the provider's signing key, yielding full impersonation of an arbitrary user at the affected application. Only applications using oidcc as an OpenID Connect relying party and processing encrypted ID tokens or JARM responses are exposed; UserInfo responses are unaffected because encryption without signing is permitted there by OpenID Connect Core 1.0 section 5.3.2. The flaw is rated 7.6 (High) under CVSS 4.0, has a 0.1% EPSS probability of exploitation in the next 30 days, is not in CISA KEV, and no public proof-of-concept or in-the-wild exploitation is currently known.

What to do: Upgrade to oidcc 3.9.0 or later. As an interim mitigation, configure relying parties to require signed-then-encrypted (nested) ID tokens and disable JARM response handling, since deployments that do not accept encrypted ID tokens or JARM responses are unlikely to be impacted. Audit your applications to confirm whether encrypted ID token or JARM validation is enabled before prioritizing patching.