# CVE-2026-70656: Checkmate ReDoS in HTTP monitor regex validation

Source: https://junglewise.ai/threats/cve-2026-70656-checkmate-redos-in-http-monitor-regex-validation  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-08-21. Updated: 2026-09-25  
License: CC BY 4.0 with a link back

CVE-2026-70656 · Severity: medium · CVSS 4.9 · Published 2026-08-21

Checkmate is an open-source server monitoring platform that tracks uptime and performance metrics. An authenticated administrator can trigger a Regular Expression Denial of Service (ReDoS) attack by configuring a malicious regex pattern in HTTP monitors, causing the application to freeze and become unresponsive to all users.

## Quick answers

**Is CVE-2026-70656 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-70656 being exploited in the wild.

**How severe is CVE-2026-70656?** Medium severity, with a CVSS score of 4.9, published 21 August 2026.

**Which products and versions are affected?** Blue Wave Labs Checkmate 3.5.1 to 3.9.1.

**Is there a fix for CVE-2026-70656?** A patch was published on 2026-08-21: Version 3.9.2 resolves the vulnerability Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

**How is CVE-2026-70656 attacked?** It is attacked over the network, in a web application.

**Am I affected by CVE-2026-70656?** Check whether anything you run is named in the advisory. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

## Technical details

The vulnerability is a Regular Expression Denial of Service (ReDoS) affecting regex-based HTTP monitor matching in Checkmate versions 3.5.1 through 3.9.1. Vulnerable code in server/src/api/validation/monitorValidation.ts accepts user-supplied regex expressions, which are then evaluated synchronously by AdvancedMatcher.ts against attacker-controlled HTTP response bodies on Node.js's main event loop without timeout or worker isolation. Catastrophic backtracking in the regex engine causes the thread to hang indefinitely, freezing API endpoints, monitor checks, and WebSocket connections for all users. Authentication as admin or superadmin is required to exploit this vulnerability. The issue is resolved in version 3.9.2 by switching to the re2 regex library and tightening validation rules.

## Affected products

- Blue Wave Labs Checkmate 3.5.1 to 3.9.1

## Timeline

- 2026-08-21: disclosed
- 2026-08-21: patched: Version 3.9.2 resolves the vulnerability

## References

- [https://github.com/bluewave-labs/Checkmate/commit/0df71d6356c87c747e0b796b0c34e33f2a5203fa](https://github.com/bluewave-labs/Checkmate/commit/0df71d6356c87c747e0b796b0c34e33f2a5203fa)
- [https://github.com/bluewave-labs/Checkmate/commit/adba25269c455878bf8065bc28cfe5d74e58692f](https://github.com/bluewave-labs/Checkmate/commit/adba25269c455878bf8065bc28cfe5d74e58692f)