---
id: CVE-2026-72704
title: >-
  The guard checker in Rocq Prover does not recheck the recursive tree
  representation of an inductive type parameter after that parameter has been
  changed by transport
summary: >-
  The guard checker in Rocq Prover does not recheck the recursive tree
  representation of an inductive type parameter after that parameter has been
  changed by transport. A fixpoint may apply a rewrite along an equality between
  types to its …
severity: medium
cvss: 6.3
cvssVector: 'CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:C/C:N/I:H/A:N'
cwe:
  - CWE-670
published: '2026-08-24'
updated: '2026-09-08'
sourceUpdated: '2026-09-08T20:23:49.880'
source: NVD
sourceUrl: 'https://nvd.nist.gov/vuln/detail/CVE-2026-72704'
references:
  - url: 'https://github.com/endrazine/rocq-cve-poc-22024'
    label: disclosure@vulncheck.com
  - url: 'https://github.com/rocq-prover/rocq'
    label: disclosure@vulncheck.com
  - url: 'https://github.com/rocq-prover/rocq/issues/22024'
    label: disclosure@vulncheck.com
  - url: 'https://github.com/rocq-prover/rocq/pull/22027'
    label: disclosure@vulncheck.com
  - url: >-
      https://www.vulncheck.com/advisories/rocq-prover-through-guard-checker-trusts-corrupted-recursive-tree-after-transport
    label: disclosure@vulncheck.com
tags:
  - nvd
  - cve.org
  - exploit-available
epss: 0.00176
epssPercentile: 0.06331
ingestedAt: '2026-09-08T21:11:12.285Z'
vendor: rocq-prover
product: rocq
affected:
  - rocq <= 9.2.0
exploitAvailable: true
ssvc:
  exploitation: poc
  automatable: 'no'
  technicalImpact: partial
  timestamp: '2026-08-25T16:37:22.786826Z'
---

## Overview

The guard checker in Rocq Prover does not recheck the recursive tree representation of an inductive type parameter after that parameter has been changed by transport. A fixpoint may apply a rewrite along an equality between types to its recursive argument, which the guard checker accepts because the inductive type is preserved, while the recursive tree recorded for the parameter is altered. A second fixpoint that calls the first inherits the altered recursive tree without verification, so a call that is not structurally decreasing is accepted as terminating. The resulting non-terminating definition proves that a natural number equals its own successor and therefore False, from which any proposition follows. The demonstration uses two axioms that follow from univalence and are consistent with the calculus of inductive constructions, so the contradiction comes from the guard check rather than from the assumptions. A fix is proposed but not merged.

## Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.