Lean 4 CVE-2024-14484 Kernel Soundness Bug: Inference Cache Poisoning POC

Vulnerability Overview Vulnerability Name: Lean 4 Kernel Soundness Bug — Inference Cache Poisoning Vulnerability ID: CVE-2024-14484 Vulnerability Type: CWE-488 (Exposure of Data Element to Wrong Session), CWE-20 (Improper Input Validation) Description: The path in the Lean 4 kernel fails to invoke , resulting in a missing closure check in declaration bodies. An attacker can exploit stale entries in the inference cache by constructing specific type expressions, thereby bypassing type checks. This allows the kernel to accept a type constant, enabling the proof of . Scope of Impact Affected Versions: Lean 4 ≤ v4.31.0 and all earlier versions. Fixed Versions: nightly 2026-07-23+, backported to v4.32.1 and v4.33.0. CVSS 3.1: AV:L/AC:L/PR:N/UI:R/S:C/C:N/I:N/A:N — 7.1 Impact Systems: Any system that trusts the Lean kernel to verify the validity of proofs, including formal verification software, cryptographic libraries, smart contracts, and safety-critical systems such as aviation and automotive. Impact Code: Malicious dependencies can silently introduce incorrect declarations within Lake packages, affecting downstream code usage. Independent Checker: The reporter confirmed that replay also accepts this exploit. The verifier export format cannot express , so verification paths remain unaffected. AI-Generated Proofs: Systems using Lean as a trusted backend (such as AlphaProof, DeepSeek-Prover, and Kimina-Prover) may generate proofs that exploit this kernel vulnerability. Remediation Fix Commit: leangprover/lean4#14498 Fix Content: Added closure checks to the function to ensure values are validated before type checking. POC Code git clone https://github.com/leanprover/lean4.git cd lean4 make -j8 lake exe cache get lake build lake run -- -trust=0 src/lean4/examples/CachePoisonFalse.lean git clone https://github.com/leanprover/lean4.git cd lean4 make -j8 lake exe cache get lake build lake run -- -trust=0 src/lean4/examples/CachePoisonFalse.lean git clone https://github.com/leanprover/lean4.git cd lean4 make -j8 lake exe cache get lake build lake run -- -trust=0 src/lean4/examples/CachePoisonFalse.lean git clone https://github.com/leanprover/lean4.git cd lean4 make -j8 lake exe cache get lake build lake run -- -trust=0 src/lean4/examples/CachePoisonFalse.lean git clone https://github.com/leanprover/lean4.git cd lean4 make -j8 lake exe cache get lake build lake run -- -trust=0 src/lean4/examples/CachePoisonFalse.lean git clone https://github.com/leanprover/lean4.git cd lean4 make -j8 lake exe cache get lake build lake run -- -trust=0 src/lean4/examples/CachePoisonFalse.lean git clone https://github.com/leanprover/lean4.git cd lean4 make -j8 lake exe cache get lake build lake run -- -trust=0 src/lean4/examples/CachePoisonFalse.lean git clone https://github.com/leanprover/lean4.git cd lean4 make -j8 lake exe cache get lake build lake run -- -trust=0 src/lean4/examples/CachePoisonFalse.lean git clone https://github.com/leanprover/lean4.git cd lean4 make -j8 lake exe cache get lake build lake run -- -trust=0 src/lean4/examples/CachePoisonFalse.lean git clone https://github.com/leanprover/lean4.git cd lean4 make -j8 lake exe cache get lake build lake run -- -trust=0 src/lean4/examples/CachePoisonFalse.lean git clone https://github.com/leanprover/lean4.git cd lean4 make -j8 lake exe cache get lake build lake run -- -trust=0 src/lean4/examples/CachePoisonFalse.lean ``` Expected Output The proof should fail with a soundness error, indicating that the kernel has accepted an invalid proof. Notes This proof relies on a specific bug in Lean 4's kernel. The bug has been fixed in the latest nightly build. To verify the fix, run the proof on a patched version of Lean 4. References Lean 4 GitHub Repository

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Lean 4 CVE-2024-14484 Kernel Soundness Bug: Inference Cache Poisoning POC

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