CVE-2026-72705: Rocq Prover before 9.2.0 Guard Checker Accepts Fixpoint Passed as a Higher-Order Argument
The guard checker in Rocq Prover does not follow recursive calls made through a fixpoint's own arguments. A fixpoint may pass itself as a higher-order argument to a second fixpoint, which then applies it to a value that is not a subterm of the structural argument. Passing the recursive function to a plain definition is rejected because the checker unfolds the definition and observes the call, but passing it to a fixpoint is accepted because higher-order recursive calls through fixpoint arguments are not tracked. This admits a type that is definitionally equal to its own negation, so self-application produces False in purely definitional code, without tactics, axioms, plugins or unsafe flags, and Print Assumptions reports the result as closed under the global context. Fixed in Rocq 9.2.0.
Affected Software
Remediation
Recommended actions to resolve this vulnerability, in priority order.
- Upgrade
Upgrade
Rocq Prover (guard checker)to a version that resolves this vulnerability.Fixed in 9.2.0
Event History
Frequently Asked Questions
Which deployments are affected?
Rocq Prover versions before 9.2.0 are affected. The issue is in the guard checker and can admit an inconsistency in purely definitional code.
What does an attacker need to exploit this?
Exploitation requires local access and user interaction, as reflected by the AV:L and UI:R vector. The proof code does not require tactics, axioms, plugins, or unsafe flags.
How can I tell whether a development has been affected?
A vulnerable construction can derive False while Print Assumptions reports the result as closed under the global context. Review untrusted or imported proof developments for fixpoints that pass themselves as higher-order arguments to another fixpoint.
What should I do if I cannot upgrade immediately?
Do not treat proofs from affected versions as sound when they include untrusted code. Review or restrict imported developments that use higher-order fixpoint arguments, especially where a recursive function is passed to another fixpoint.