# CVE-2026-55591

## Summary

- **CVE ID:** CVE-2026-55591
- **Severity:** MEDIUM
- **CVSS Score:** 5.8 (CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:L/I:N/A:N)
- **CWE:** CWE-918
- **Published:** Sep 15, 2026
- **Last Modified:** Sep 15, 2026

## Description

Signal K Server is a server application that runs on a central hub in a boat. Prior to 2.28.0, makeRemoteRequest() in src/serverroutes.ts accepted attacker-controlled host, port, useTLS, and selfsignedcert parameters from the testSignalKConnection, requestAccess, and checkAccessRequest endpoints without validating the destination. When security was not configured, addAdminMiddleware() was a no-op in dummysecurity.ts, leaving all three endpoints accessible without authentication. The server could be forced to contact loopback, private, link-local, cloud metadata, or arbitrary external destinations, and selfsignedcert could disable certificate verification for outbound HTTPS requests. The checkAccessRequest endpoint also interpolated requestId into its destination path, allowing traversal to other paths on the selected host. Distinct success, connection-refused, and timeout responses enabled internal port scanning; returned response bodies enabled cloud metadata and internal-service data exfiltration; requestAccess enabled server-side POST requests with attacker-controlled JSON; and access to cluster-internal services could support lateral movement. This issue is fixed in version 2.28.0.

## Affected Products

- SignalK — signalk-server (< 2.28.0)

## References

- [CNA](https://github.com/SignalK/signalk-server/security/advisories/GHSA-q59x-jc9f-gfqf)
- [CNA](https://github.com/SignalK/signalk-server/commit/2816b0dda1bdde893d85c969a9c5950e7825eee7)
- [CNA](https://github.com/SignalK/signalk-server/releases/tag/v2.28.0)

## Exploitation Prediction (EPSS)

- **EPSS Score:** 0.27%
- **EPSS Percentile:** 20.0

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_Exported from OnDuty AI Vulnerability Intelligence on 2026-09-19._