CVE-2026-119283: joserfc: Unbounded JWE General JSON `recipients` Array Leads to CPU Exhaustion (DoS) via Repeated RSA Private-Key Decryption

joserfc.jwe.decrypt_json(), the library’s public parser for JWE General JSON Serialization, accepts an attacker-controlled recipients array of unbounded length and performs one full private-key decryption operation (decrypt_cek) for every recipient present in the input, with no cap on recipient count. An unauthenticated network attacker who can send a JWE General JSON document to any endpoint that decrypts it with an RSA key (e.g. RSA-OAEP) can force the victim to perform an arbitrary, attacker-chosen number of RSA private-key decryption operations from a single, relatively small HTTP request. This gives the attacker a highly asymmetric CPU-exhaustion (Denial of Service) primitive: local reproduction shows request size growing linearly with recipient count (~396 bytes/recipient) while server-side CPU time grows in lock-step (near 1:1 ratio between recipient-count growth and decrypt-time growth), and the library’s only documented mitigation knob, verify_all_recipients=False, does not reduce the CPU cost, since the decrypt loop attempts every recipient’s decrypt_cek() unconditionally before that flag is ever consulted. This is CWE-400 (Uncontrolled Resource Consumption) with CVSS v3.1 Base Score 7.5 (High).