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BREW-bbot-CVE-2026-101917 — PyJWT: PyJWKClient still amplifies unauthenticated JWKS fetches on unknown kid values (incomplete fix of CVE-2026-48524)

Affected: Homebrew: bbot

Summary CVE-2026-48524 (GHSA-fhv5-28vv-h8m8, "PyJWKClient unbounded JWKS endpoint requests via attacker-controlled kid values (DoS)") was fixed in 2.13.0 by stopping fetch_data() from clearing the cache on a fetch error. That closed one amplification path but did not add the mitigation the advisory's title implies: there is still no rate-limit, negative-cache, or minimum-refresh-interval for unknown kids.

At HEAD, get_signing_key(kid) (jwt/jwks_client.py:185-211), on any unknown kid, calls get_signing_keys(refresh=True), and refresh=True bypasses jwk_set_cache unconditionally and forces a fresh fetch_data(). The kid is read from the unverified token header (get_signing_key_from_jwt decodes with verify_signature=False), so no valid token and no authentication is required. lru_cache does not cache the raised exception, so even the same unknown kid repeated re-fetches on every call.

Affected pyjwt <= 2.13.0 (the latest release; the patched release for CVE-2026-48524). No fixed version yet.

Proof of concept (verified on 2.13.0, cache enabled = realistic prod config) import threading, http.server, socketserver, json from jwt import PyJWKClient hits = {'n': 0} JWKS = json.dumps({"keys":[{"kty":"oct","kid":"real","k":"AAAA"}]}).encode() class H(http.server.BaseHTTPRequestHandler): def do_GET(self): hits['n'] += 1 self.send_response(200); self.send_header('Content-Type','application/json'); self.end_headers() self.wfile.write(JWKS) def log_message(…

fkie_cve-2026-101917

PyJWT is a Python implementation of JSON Web Token standards. Prior to 2.14.0, PyJWT get_signing_key_from_jwt is affected because unknown kid misses force refreshes without a negative cache or minimum refresh interval. This occurs when unauthenticated tokens repeatedly use the same unknown kid or varying kid values absent from the cached JWKS. As a result, each cache miss causes PyJWKClient to refresh the JWKS. Consequently, attacker traffic can amplify outbound requests to the configured JWKS endpoint. This issue is fixed in version 2.14.0.

GHSA-2gx3-rcp4-g85q — PyJWT: PyJWKClient still amplifies unauthenticated JWKS fetches on unknown kid values (incomplete fix of CVE-2026-48524)

Affected: PyPI: pyjwt

Affected pyjwt <= 2.13.0 (the latest release; the patched release for CVE-2026-48524). No fixed version yet.

msrc_CVE-2026-101917 — PyJWT: PyJWKClient still amplifies unauthenticated JWKS fetches on unknown kid values (incomplete fix of CVE-2026-48524)

msrc_CVE-2026-101917

UBUNTU-CVE-2026-101917

Affected: Ubuntu:Pro:16.04:LTS: pyjwt, Ubuntu:Pro:18.04:LTS: pyjwt, Ubuntu:Pro:20.04:LTS: pyjwt, Ubuntu:22.04:LTS: pyjwt, Ubuntu:24.04:LTS: pyjwt, Ubuntu:26.04:LTS: pyjwt