CVE-2026-65628: Infinite recursion (CPU denial-of-service) in JOSE.JWK.shared_secret/2 on mismatched key types

josejwk:sharedsecret/2 (exposed in Elixir as JOSE.JWK.sharedsecret/2) derives an ECDH shared secret from two JWKs. Its first function clause only matches when both JWKs carry the same key type (kty) module, and its fallback clause re-invokes itself as sharedsecret(from(YourJWK), from(MyJWK)). Because from/1 returns an already-parsed josejwk record unchanged, passing two JWKs whose key types differ (for example an EC key and an RSA key) makes the fallback clause re-enter with identical arguments, producing an unbounded tail-recursive loop that never returns and never crashes.

An application that derives a shared secret from an externally supplied peer public key without first checking that the peer key's type and curve match its own key can be driven into this loop by an attacker-controlled JWK, pinning an Erlang scheduler at 100% CPU. Repeated requests exhaust the available schedulers, resulting in a denial of service.

This issue affects jose: from 1.5.0 before 1.11.13.