# CVE-2026-70656: Checkmate: Regular Expression Denial of Service (ReDoS) via User-Controlled Regex in Monitor Advanced Matching

> An authenticated admin can cause a denial of service by submitting a malicious regex in monitor settings, freezing the application for all users.

- **Severity:** Medium 4.9 (`CVSS:3.1/AV:N/AC:L/PR:H/UI:N/S:U/C:N/I:N/A:H`)
- **Exploited in the wild:** Not known
- **Login needed:** An administrator
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** No
- **Published:** 21 Aug 2026
- **Updated:** 21 Aug 2026
- **Also known as:** GHSA-4c6j-p2cv-wf56

## What is CVE-2026-70656?

CVE-2026-70656 is a medium-severity denial of service vulnerability in bluewave-labs Checkmate, published on 21 Aug 2026. An attacker needs administrator access to exploit it, with no action from the victim.

### Official 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.

Weakness: CWE-1333 (Inefficient Regular Expression Complexity)

## Which versions are affected by CVE-2026-70656?


## How do I fix CVE-2026-70656?

No fix has been published for CVE-2026-70656 yet. Limit exposure of the affected software until one is available.

## Is CVE-2026-70656 being exploited?

It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-70656 exists.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-70656 and fix it if it is affected.

What it is: CVE-2026-70656 is a medium-severity denial of service vulnerability in bluewave-labs Checkmate, published on 21 Aug 2026. An attacker needs administrator access to exploit it, with no action from the victim.
Exploitation: It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-70656 exists.

Affected product: bluewave-labs Checkmate. No package-level version data is available, so check the vendor advisory linked from the reference page.

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-70656/ (Markdown: https://insights.sbomify.com/CVE-2026-70656/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-70656
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-70656
- OSV: https://osv.dev/vulnerability/CVE-2026-70656

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-70656/
Summaries are generated and may contain mistakes; the official description above is the record.