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Fri, 21 Aug 2026 22:30:00 +0000
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ssvc
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Fri, 21 Aug 2026 13:30:00 +0000
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| First Time appeared |
Leanprover
Leanprover lean4 |
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| Vendors & Products |
Leanprover
Leanprover lean4 |
Thu, 20 Aug 2026 17:30:00 +0000
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| Description | The Lean 4 kernel does not verify that the structure named in a projection expression matches the type of the value being projected, and environment::add_inductive in src/kernel/inductive.cpp did not type check the nested inductive applications that are replaced by auxiliary types, so their parametric arguments escaped checking. A metaprogram running in the Lean process can register an ill-typed nested inductive whose constructor applies a .proj C 0 projection to a value of the unrelated type W, and the kernel admits the declaration through the ordinary checked addDecl path at maximum kernel checking, without sorry, unsafeCast, debug.skipKernelTC, addDeclWithoutChecking, FFI, or a modified .olean file. The result is a type confusion yielding a proof of False that carries no axioms, from which any proposition can be derived. The published proof of concept additionally pads two expressions until their hashes and approximate depths collide, which defeats kernel caching; that is the technique used to reach the flaw, not its cause. Exploitation requires running a metaprogram in-process, for example by building a project or importing a malicious Lake dependency. | |
| Title | Lean 4 Kernel Type Checking Bypass via Mismatched Structure Projections | |
| Weaknesses | CWE-843 | |
| References |
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| Metrics |
cvssV3_1
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Projects
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Status: PUBLISHED
Assigner: VulnCheck
Published:
Updated: 2026-08-21T21:46:54.936Z
Reserved: 2026-08-10T15:14:51.467Z
Link: CVE-2026-72844
Updated: 2026-08-21T21:13:57.269Z
Status : Received
Published: 2026-08-20T18:16:45.290
Modified: 2026-08-21T22:16:44.447
Link: CVE-2026-72844
No data.
OpenCVE Enrichment
Updated: 2026-08-21T13:01:24Z