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.
CVE-2026-72844
“—” beside the score: it is equal to the CVSS score beside it.
Score 6.3 from GitHub Security Advisory published 2026-08-20. A secondary CVSS source baseline 6.3; sources differ by 0.0.
Also known asEUVD-2026-63487 (ENISA EUVD) · GHSA-4fhc-8rq3-cjvg (GitHub Security Advisories)Source: ENISA EUVD
- Public exploit or proof-of-concept code is available
An upstream fix is merged but not yet released — mitigate (WAF / firewall / segmentation) until the release ships, then apply it.
- CVSS v3
- 6.3
- EG Score
- 6.3MEDIUMmedium confidence
- EG Risk
- 44EG Risk 44/100
EG Risk is EchelonGraph's 0–100 priority score. It fuses impact severity (EG Severity, the CVSS base score, never the KEV-floored or EPSS-lifted EG Score) with real-world exploitation and automatability, under weights EchelonGraph set by hand, so you can rank equal-severity CVEs and fix the most dangerous first. Higher = act sooner.
How it’s computed (value × EchelonGraph’s weight)Severity63% × 45%Impact severity (EG Severity): CVSS 6.3 of 10. Never the KEV-floored or EPSS-lifted EG Score.Exploitation40% × 40%EchelonGraph's fixed weight for EG-KEV Tier 3 (Elevated): a constant, not a probability.Automatability0% × 15%CISA's SSVC Automatable value: no (Vulnrichment).SSVC (CISA's decision table, applied by EchelonGraph): Track at low or medium mission impact; Track* at high (mission-essential systems).Exploitation public PoC (CISA Vulnrichment) · Automatable no (CISA Vulnrichment) · Technical impact partial (CISA Vulnrichment). All three are CISA's SSVC values (Vulnrichment). EchelonGraph applied CISA's decision table to them; CISA publishes SSVC inputs and the table, not a decision for each CVE.Action: An upstream fix is merged but not yet in a tagged release. Until the release ships, restrict network exposure of the affected system or apply the vendor's mitigation on your normal schedule, then apply it. - EPSS PROB
- 0.2%
- EPSS %ILE
- 8th
- KEV
- Not listed
What the EG score is made of (scorer v4.0: the three questions the 0–10 score mixes, published apart · methodology)
The EG score (6.3): severity, escalated by confirmed exploitation. This CVE's 6.3 is its impact severity (EG Severity), not escalated.
- EG Severity
- 6.3 MEDIUMCVSS-B, impact only: no KEV listing, EPSS or EG-KEV tier raises it.GitHub Security Advisory CVSS
- EG Likelihood
- 0.2% within 30 daysSource: FIRST EPSS (model v2026.06.15, score date 2026-10-29). FIRST's exploitation probability, not an EchelonGraph model.
- Confirmed exploitation
- None on record (CISA KEV, EG-KEV Tier 1)Reported apart from the likelihood: an observed fact, not a probability.
- EG Priority
- SSVC Track at medium mission impactTrack at low or medium mission impact; Track* at high (mission-essential systems).CISA BOD 26-04: 60 days if the affected system is publicly exposed; Fix on system upgrade if it is not.No released fix is confirmed on this page, but CISA's timeline does not wait for a fix's release: it starts when an agency identifies the flaw on an asset and updates the CDM Agency and Federal Dashboard, and the directive counts patching, decommissioning the system or another action as remediation. Until a fixed release is applied, mitigate as this page's verdict says. In the directive's words, “Fix on system upgrade” means that, “unless conditions change”, the vulnerability “should be remediated the next time the vulnerable asset receives a scheduled major upgrade or rebuild”: its timelines are “dynamic as facts change”, and a KEV listing shortens them.Each input and its source, and whom BOD 26-04 binds: the SSVC and BOD 26-04 blocks below.
SSVC (CISA's decision table, applied by EchelonGraph)Track at low or medium mission impact; Track* at high (mission-essential systems).
An upstream fix is merged but not yet in a tagged release. Until the release ships, restrict network exposure of the affected system or apply the vendor's mitigation on your normal schedule, then apply it.
Exploitation public PoC (CISA Vulnrichment) · Automatable no (CISA Vulnrichment) · Technical impact partial (CISA Vulnrichment). All three are CISA's SSVC values (Vulnrichment). EchelonGraph applied CISA's decision table to them; CISA publishes SSVC inputs and the table, not a decision for each CVE. Mission impact is CISA's Mission & Well-being decision point, and only you can judge it. CISA's table makes it high when Mission Prevalence is Essential — the vulnerable component "directly provides capabilities that constitute at least one MEF for at least one entity" (MEF: mission essential function) — or when Public Well-Being Impact is Irreversible: "multiple fatalities are likely", the cyber-physical system "is likely lost or destroyed", "extreme or serious externalities" are imposed on other parties, or social systems such as elections or the financial grid "are destabilized and potentially collapse". CISA's decision table
BOD 26-04 (CISA's remediation timeline, Table 1)60 days if the affected system is publicly exposed; Fix on system upgrade if it is not.
No released fix is confirmed on this page, but CISA's timeline does not wait for a fix's release: it starts when an agency identifies the flaw on an asset and updates the CDM Agency and Federal Dashboard, and the directive counts patching, decommissioning the system or another action as remediation. Until a fixed release is applied, mitigate as this page's verdict says. In the directive's words, “Fix on system upgrade” means that, “unless conditions change”, the vulnerability “should be remediated the next time the vulnerable asset receives a scheduled major upgrade or rebuild”: its timelines are “dynamic as facts change”, and a KEV listing shortens them.
The score's inputs: In CISA KEV no (CISA's KEV catalog) · Automatable no (CISA Vulnrichment) · Technical impact partial (CISA Vulnrichment). Whether your system is publicly exposed is yours to answer. BOD 26-04 binds US Federal Civilian Executive Branch agencies; for anyone else it is CISA's published timeline, a reference rather than an obligation. The directive · how EchelonGraph applies it
Published
August 20, 2026
Last Modified
October 26, 2026
Advisory Details (8)
Auto-updated Aug 20, 2026Lean 4 Kernel Type Checking Bypass via Mismatched Structure Projections | Advisories | VulnCheck
https://www.vulncheck.com/advisories/lean-4-kernel-type-checking-bypass-via-mismatched-structure-projectionsGitHub - leanprover/lean4: Lean 4 programming language and theorem prover · GitHub
https://github.com/leanprover/lean4oss-security - Lean 4 kernel soundness bug: forging proofs via nested inductive projections (0 = 1 demonstrated)
https://www.openwall.com/lists/oss-security/2026/08/02/1GitHub - xrchz/CollatzLean: Collatz conjecture in Lean · GitHub
https://github.com/xrchz/CollatzLeanGitHub - endrazine/lean-cve-poc: Example of proving "0 = 1" using a vulnerability in the Lean 4 kernel. · GitHub
https://github.com/endrazine/lean-cve-pocfix: missing check at kernel inductive declaration
Fix merged in leanprover/lean4 PR #14577 on 2026-07-28 — awaiting tagged release
https://github.com/leanprover/lean4/pull/14577commit a39eab69e1ee (leanprover/lean4)
Fix landed in leanprover/lean4 commit a39eab69e1ee — awaiting tagged release
https://github.com/leanprover/lean4/commit/a39eab69e1eee9ad38f4efe507907b1026a77808Kernel accepts wrong-structure projections, allowing an axiom-free proof of False · Issue #14576 · leanprover/lean4 · GitHub
https://github.com/leanprover/lean4/issues/14576Vendor Advisories for CVE-2026-72844(1)
These vendors published their own advisory mentioning this CVE — often with vendor-specific remediation steps + affected product lists not in NVD.
Weakness Classification(1)
MITRE Common Weakness Enumeration — the root-cause categories this CVE belongs to.
Data Freshness Timeline
(refreshed 9× in last 7d / 53× in last 30d)
Each row is a time one of our pipelines fetched, updated or re-scored this CVE. For example, "NVD update" means NVD published or revised its analysis for this CVE; "MITRE cvelistV5" means we ingested or refreshed it from the CNA feed. An arrow marks a change the record states ("CVSS v3 → 9.1"); EPSS and GHSA rows show the values recorded at that time, not what changed (EPSS values are rounded; hover one for the exact figures). Most recent first.
Showing the most recent 99 of 173 refreshes on record for this CVE.
A repeat, a row identical to one the same pipeline wrote less than 10 seconds earlier, is not a separate refresh and is not counted. 1 repeat row among the latest 100 is merged into the row it repeats. The 74 oldest rows on record are not shown and were not checked, so the counts can still include repeats.
- 2026-11-02 16:46 UTCEPSS rescoreEPSS 0.2% · 8th percentile
- 2026-11-01 16:35 UTCEPSS rescoreEPSS 0.2% · 8th percentile
- 2026-10-31 16:33 UTCEPSS rescoreEPSS 0.2% · 8th percentile
- 2026-10-30 16:35 UTCEPSS rescoreEPSS 0.2% · 8th percentile
- 2026-10-29 16:59 UTCEG score recompute
- 2026-10-29 16:59 UTCGHSA enrichmentGHSA-4fhc-8rq3-cjvg · GitHub CVSS 6.3
- 2026-10-29 16:34 UTCEPSS rescoreEPSS 0.2% · 8th percentile
- 2026-10-28 16:33 UTCEPSS rescoreEPSS 0.2% · 8th percentile
- 2026-10-27 16:32 UTCEPSS rescoreEPSS 0.2% · 8th percentile
- 2026-10-26 16:32 UTCEPSS rescoreEPSS 0.2% · 8th percentile
- 2026-10-26 02:26 UTCEG score recompute
- 2026-10-26 02:26 UTCGHSA enrichmentGHSA-4fhc-8rq3-cjvg · GitHub CVSS 6.3
- 2026-10-26 01:46 UTCEG score recompute
- 2026-10-26 01:46 UTCGHSA enrichmentGHSA-4fhc-8rq3-cjvg · GitHub CVSS 6.3
- 2026-10-25 16:33 UTCEPSS rescoreEPSS 0.2% · 7th percentile
- 2026-10-25 14:06 UTCEG score recompute
- 2026-10-24 16:33 UTCEPSS rescoreEPSS 0.2% · 6th percentile
- 2026-10-23 16:32 UTCEPSS rescoreEPSS 0.2% · 6th percentile
- 2026-10-22 16:35 UTCEPSS rescoreEPSS 0.2% · 6th percentile
- 2026-10-21 16:33 UTCEPSS rescoreEPSS 0.2% · 6th percentile
- 2026-10-20 16:33 UTCEPSS rescoreEPSS 0.2% · 6th percentile
- 2026-10-19 16:33 UTCEPSS rescoreEPSS 0.2% · 6th percentile
- 2026-10-18 20:36 UTCEG score recompute
- 2026-10-18 20:36 UTCGHSA enrichmentGHSA-4fhc-8rq3-cjvg · GitHub CVSS 6.3
- 2026-10-18 16:32 UTCEPSS rescoreEPSS 0.2% · 6th percentile
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- 2026-10-18 03:15 UTCEG score recompute
- 2026-10-17 16:35 UTCEPSS rescoreEPSS 0.2% · 6th percentile
- 2026-10-16 16:44 UTCEPSS rescoreEPSS 0.2% · 6th percentile
- 2026-10-15 16:32 UTCEPSS rescoreEPSS 0.2% · 6th percentile
- 2026-10-14 16:33 UTCEPSS rescoreEPSS 0.2% · 6th percentile
- 2026-10-13 16:35 UTCEPSS rescoreEPSS 0.2% · 6th percentile
- 2026-10-12 15:41 UTCEG score recompute
- 2026-10-11 19:27 UTCEG score recompute
- 2026-10-11 16:42 UTCEG score recompute
- 2026-10-11 14:02 UTCEG score recompute
- 2026-10-11 13:49 UTCEPSS rescoreEPSS 0.2% · 6th percentile
- 2026-10-10 20:00 UTCEPSS rescoreEPSS 0.2% · 6th percentile
- 2026-10-09 20:07 UTCEPSS rescoreEPSS 0.2% · 6th percentile
- 2026-10-08 17:13 UTCEPSS rescoreEPSS 0.2% · 6th percentile
- 2026-10-08 05:24 UTCEG score recompute
- 2026-10-08 05:23 UTCGHSA enrichmentGHSA-4fhc-8rq3-cjvg · GitHub CVSS 6.3
- 2026-10-07 23:48 UTCEPSS rescoreEPSS 0.2% · 6th percentile
- 2026-10-07 02:13 UTCEG score recompute
- 2026-10-07 02:13 UTCGHSA enrichmentGHSA-4fhc-8rq3-cjvg · GitHub CVSS 6.3
- 2026-10-06 15:18 UTCEPSS rescoreEPSS 0.2% · 6th percentile
- 2026-10-06 03:27 UTCEG score recompute
- 2026-10-06 03:27 UTCGHSA enrichmentGHSA-4fhc-8rq3-cjvg · GitHub CVSS 6.3
- 2026-10-05 17:43 UTCEPSS rescoreEPSS 0.2% · 6th percentile
- 2026-10-05 01:50 UTCEG score recompute
- 2026-10-05 01:50 UTCGHSA enrichmentGHSA-4fhc-8rq3-cjvg · GitHub CVSS 6.3
- 2026-10-04 23:22 UTCEPSS rescoreEPSS 0.2% · 6th percentile
- 2026-10-04 03:30 UTCEG score recompute
- 2026-10-04 03:30 UTCGHSA enrichmentGHSA-4fhc-8rq3-cjvg · GitHub CVSS 6.3
- 2026-10-03 14:26 UTCEPSS rescoreEPSS 0.2% · 6th percentile
- 2026-10-03 05:09 UTCEG score recompute
- 2026-10-03 05:09 UTCGHSA enrichmentGHSA-4fhc-8rq3-cjvg · GitHub CVSS 6.3
- 2026-10-02 06:49 UTCEG score recompute
- 2026-10-02 06:49 UTCGHSA enrichmentGHSA-4fhc-8rq3-cjvg · GitHub CVSS 6.3
- 2026-10-01 19:50 UTCEPSS rescoreEPSS 0.2% · 6th percentile
- 2026-10-01 06:34 UTCEG score recompute
- 2026-10-01 06:34 UTCGHSA enrichmentGHSA-4fhc-8rq3-cjvg · GitHub CVSS 6.3
- 2026-09-30 08:14 UTCEG score recompute
- 2026-09-30 08:14 UTCGHSA enrichmentGHSA-4fhc-8rq3-cjvg · GitHub CVSS 6.3
- 2026-09-28 23:42 UTCEG score recompute
- 2026-09-28 23:42 UTCGHSA enrichmentGHSA-4fhc-8rq3-cjvg · GitHub CVSS 6.3
- 2026-09-28 13:52 UTCEPSS rescoreEPSS 0.2% · 6th percentile
- 2026-09-28 01:22 UTCEG score recompute
- 2026-09-28 01:22 UTCGHSA enrichmentGHSA-4fhc-8rq3-cjvg · GitHub CVSS 6.3
- 2026-09-27 13:48 UTCEPSS rescoreEPSS 0.2% · 6th percentile
- 2026-09-27 03:02 UTCEG score recompute
- 2026-09-27 03:02 UTCGHSA enrichmentGHSA-4fhc-8rq3-cjvg · GitHub CVSS 6.3
- 2026-09-26 15:59 UTCEPSS rescoreEPSS 0.2% · 6th percentile
- 2026-09-24 21:21 UTCEG score recompute
- 2026-09-24 21:21 UTCGHSA enrichmentGHSA-4fhc-8rq3-cjvg · GitHub CVSS 6.3
- 2026-09-24 02:52 UTCEG score recompute
- 2026-09-24 02:52 UTCGHSA enrichmentGHSA-4fhc-8rq3-cjvg · GitHub CVSS 6.3
- 2026-09-23 17:54 UTCEPSS rescoreEPSS 0.2% · 8th percentile
- 2026-09-23 04:31 UTCEG score recompute
- 2026-09-23 04:31 UTCGHSA enrichmentGHSA-4fhc-8rq3-cjvg · GitHub CVSS 6.3
- 2026-09-22 06:11 UTCEG score recompute
- 2026-09-22 06:11 UTCGHSA enrichmentGHSA-4fhc-8rq3-cjvg · GitHub CVSS 6.3
- 2026-09-21 21:09 UTCEPSS rescoreEPSS 0.2% · 8th percentile
- 2026-09-21 07:50 UTCEG score recompute
- 2026-09-21 07:50 UTCGHSA enrichmentGHSA-4fhc-8rq3-cjvg · GitHub CVSS 6.3
- 2026-09-20 20:16 UTCEPSS rescoreEPSS 0.2% · 8th percentile
- 2026-09-20 09:01 UTCEG score recompute
- 2026-09-20 09:01 UTCGHSA enrichmentGHSA-4fhc-8rq3-cjvg · GitHub CVSS 6.3
- 2026-09-19 10:12 UTCEG score recompute
- 2026-09-19 10:12 UTCGHSA enrichmentGHSA-4fhc-8rq3-cjvg · GitHub CVSS 6.3
- 2026-09-18 19:28 UTCEPSS rescoreEPSS 0.2% · 8th percentile
- 2026-09-18 11:32 UTCEG score recompute
- 2026-09-18 11:31 UTCGHSA enrichmentGHSA-4fhc-8rq3-cjvg · GitHub CVSS 6.3
- 2026-09-17 13:10 UTCGHSA enrichmentGHSA-4fhc-8rq3-cjvg · GitHub CVSS 6.3
- 2026-09-16 14:29 UTCEG score recompute
- 2026-09-16 14:29 UTCGHSA enrichmentGHSA-4fhc-8rq3-cjvg · GitHub CVSS 6.3
- 2026-09-16 14:08 UTCEPSS rescoreEPSS 0.2% · 8th percentile
- 2026-09-16 05:15 UTCEPSS rescoreEPSS 0.2% · 8th percentile
- 2026-09-15 15:13 UTCEG score recompute
- 2026-09-15 15:13 UTCGHSA enrichmentGHSA-4fhc-8rq3-cjvg · GitHub CVSS 6.3
Publicly available exploits
(1 reference)Public exploit code is referenced for this CVE (1 GitHub PoC). The fix is not yet in a release, so defenders should restrict or isolate affected systems accordingly until it ships.
- GitHub PoCendrazine/lean-cve-pocPublished Aug 2, 2026
CVE-2026-72844 : Example of proving "0 = 1" using a vulnerability in the Lean 4 kernel.
Open source ↗
Related CVEs(same CWE)
Frequently asked(5)
What is CVE-2026-72844?
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What is the CVSS score of CVE-2026-72844?
How do I remediate CVE-2026-72844?
Dependency Blast Radius
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