CVE-2026-55241 Checkmate: Pre-auth Denial of Service via File Upload on Registration
Unauthenticated attackers can crash the Checkmate server by uploading oversized files during registration, exhausting memory resources.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- None listed
What is CVE-2026-55241?
CVE-2026-55241 is a high-severity denial of service vulnerability in bluewave-labs Checkmate, published on 21 Aug 2026. An attacker can exploit it over the internet without logging in, 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. Prior to 3.9.1, the public POST /api/v1/auth/register route in server/src/api/routes/authRoutes.ts passes multipart profileImage uploads through in-memory Multer parsing before registration validation, without file-size, file-count, or MIME-type limits in server/src/api/middleware/upload.ts. An unauthenticated attacker can submit concurrent oversized files that are buffered before invalid registration or invite-token checks reject the request, exhausting memory and crashing or destabilizing the backend. This issue is fixed in version 3.9.1.
Which versions are affected by CVE-2026-55241?
How do I fix CVE-2026-55241?
No fix has been published for CVE-2026-55241 yet. Limit exposure of the affected software until one is available.
Upgrade, then put limits on request size, rate and nesting depth so one client cannot exhaust the service. More about Denial of service.
Is CVE-2026-55241 being exploited?
It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-55241 exists.
Sources
Also known as GHSA-9xvg-x28f-m78m.