Description
Checkmate is an open-source, self-hosted tool designed to track and monitor server hardware, uptime, response times, and incidents in real-time with beautiful visualizations. From 3.5.1 until 3.9.2, an authenticated admin or superadmin can set matchMethod to regex and place a malicious expression in the expectedValue field for advanced HTTP monitor matching. server/src/api/validation/monitorValidation.ts accepts the expression, and server/src/service/network/AdvancedMatcher.ts synchronously evaluates it against an attacker-controlled HTTP response body on the Node.js main event loop without a timeout or worker isolation, allowing catastrophic backtracking to freeze API endpoints, monitor checks, and WebSocket connections for all users. This issue is fixed in version 3.9.2.
References6
- github.com/bluewave-labs/Checkmate/commit/0df71d6356c87c747e0b7…
- github.com/bluewave-labs/Checkmate/commit/adba25269c455878bf806…
- github.com/bluewave-labs/Checkmate/commit/d5ec2936ad77ab7735290…
- github.com/bluewave-labs/Checkmate/releases/tag/v3.9.2
- github.com/bluewave-labs/Checkmate/security/advisories/GHSA-4c6…
- github.com/bluewave-labs/Checkmate/security/advisories/GHSA-4c6…
Metrics
- CVSS 3.1
-
4.9
MEDIUM
Score source: CNA
CVSS:3.1/AV:N/AC:L/PR:H/UI:N/S:U/C:N/I:N/A:H - EPSS — exploit probability
- 1% percentile: 48 · as of 10 November 2026
- CWE
- CWE-1333
Could this be exploited in your environment?
A patch closes the known hole. A penetration test shows what an attacker can still reach — with proof.