CVE-2026-72844: Lean 4 kernel soundness bug — forging proofs via nested inductive projections (0 = 1 demonstrated)

Posted by Jonathan Brossard on Oct 25 1. Summary ========== A soundness bug in the Lean 4 kernel allows construction of a checked proof of False — and by extension, any proposition, including 0 = 1 — without axioms, sorry, unsafeCast, or modified .olean files. The kernel does not verify that the structure named in a projection expression matches the type of the value being projected. Additionally, environment::add_inductive in src/kernel/inductive.cpp did not type-check nested...

Published 26-Oct-2026 01:00 UTC · First seen 26-Oct-2026 00:58 UTC

Sources

• Open Source Security · 26-Oct-2026