CVE-2026-72711

The Lean 4 kernel does not check that the body of an opaque declaration is closed. environment::addopaque omits the checknometavarnofvar call that the definition and theorem paths perform, so a value containing a free variable that is absent from the local context is not rejected outright. A...

CVE-2026-72711

CVE-2026-72711 is a kernel soundness flaw in Lean 4 before 4.32.2. The function environment::add_opaque omits the check_no_metavar_no_fvar closure check that the definition and theorem paths perform. A metaprogram can exploit a stale entry in the type checker's inference cache to submit an opaque...