CVE-2026-55591 Signal K Server: Server-Side Request Forgery via Remote Connection Endpoints
Attackers can force the server to contact internal or external hosts, enabling data exfiltration and port scanning when security is unconfigured.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-55591?
CVE-2026-55591 is a medium-severity server-side request forgery vulnerability in signalk-server, published on 15 Sep 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Official 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.
Weakness: CWE-918
Which versions are affected by CVE-2026-55591?
2 open source packages ship an affected version, including signalk-server.
| Package | Affected | Fixed in |
|---|---|---|
signalk-server npm | All versions | 2.28.0 |
signalk-server npm | All versions | 2.28.0 |
How do I fix CVE-2026-55591?
Upgrade signalk-server to 2.28.0 or later.
Upgrade, and send outbound requests through an allow-list that blocks internal addresses. More about Server-side request forgery.
Is CVE-2026-55591 being exploited?
It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-55591 exists.
Sources
Also known as GHSA-q59x-jc9f-gfqf.