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TI-2026-39916 Aliases CVE-2026-55241

Checkmate: Pre-auth Denial of Service via File Upload on Registration

Priority HIGH 72CWE-400Published · Updated

Key facts

Attack vector
Network
Privileges required
None
User interaction
None
Attack complexity
Low
Impact type
Denial of service
Confidentiality · integrity · availability
None · None · High
Fix status
Fixed

Attack profile from CVSS 3.1 · CNA. Fix status from CNA. Impact type from CWE-400.

Summary

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.

Why it matters now

Exploitation Proof of concept CISA SSVC · not in CISA KEV
EPSS 0.00618 49th percentileScored 2026-11-07
Fix Fixed Checkmate (bluewave-labs): 3.9.1

SSVC decision points

CISA ADP · SSVC 2.0.3

Exploitation
Poc
Automatable
Yes
Technical impact
Partial

The decision (Track, Attend, Act) also depends on your mission and well-being impact; see CISA's SSVC guide.

Affected products

VendorProductAffected versionsFixed inStatusSource
bluewave-labsCheckmatebefore 3.9.13.9.1Patch availableCNA
  • Checkmate Vendorbluewave-labs Affected before 3.9.1 Fixed in 3.9.1 Patch available CNA

Remediation

  • Fix · CNA Checkmate (bluewave-labs) Fixed in 3.9.1

Timeline

  1. 2026-10-02 Threatist record created from CVE-2026-55241

References

Other 3

  • TI-2026-24389 Mass Assignment Privilege Escalation in Checkmate CVSS 3.1HIGH 8.1
  • TI-2026-58598 Checkmate through 3.11.0 Missing Authorization on Maintenance Window, Notification, and Check Deletion Routes CVSS 4.0HIGH 7.1
  • TI-2026-23658 Checkmate: Unauthenticated Access to Unpublished Status Page CVSS 3.1MEDIUM 5.3
  • TI-2026-49357 Checkmate: Regular Expression Denial of Service (ReDoS) via User-Controlled Regex in Monitor Advanced Matching CVSS 3.1MEDIUM 4.9
  • TI-2026-50184 Checkmate: Sensitive Bearer Token Exposure via Public Status Pages When showURL Setting is Enabled CVSS 3.1HIGH 7.5
  • TI-2026-50845 bluewave-labs Checkmate - User Enumeration via Differential HTTP Response in Password Recovery CVSS 3.1MEDIUM 5.3

Sources

This product uses the NVD API but is not endorsed or certified by the NVD. Sources and licences