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Transmission 4.0.0 before 4.1.3 contains a permissive CORS vulnerability in handlerequest() in rpc-server.cc that exposes the X-Transmission-Session-Id anti-CSRF token to any web origin. Malicious web pages can read the token from the 409 handshake response and replay it to issue RPC calls, enabling script-torrent-done execution, download-dir changes, or torrent and data deletion.
Last updated 8 June 2026