# 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.

- **Severity:** Medium 5.8 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:L/I:N/A:N`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 15 Sep 2026
- **Updated:** 15 Sep 2026
- **Also known as:** GHSA-q59x-jc9f-gfqf

## 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 (Server-Side Request Forgery)

## Which versions are affected by CVE-2026-55591?

2 open source packages ship an affected version, including signalk-server.


| Package | Ecosystem | 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.

## Is CVE-2026-55591 being exploited?

It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-55591 exists.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-55591 and fix it if it is affected.

What it is: 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.
Exploitation: It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-55591 exists.

Affected packages and fixed versions:
- signalk-server (npm): affected all versions; fixed in 2.28.0
- signalk-server (npm): affected all versions; fixed in 2.28.0

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-2026-55591/ (Markdown: https://insights.sbomify.com/CVE-2026-55591/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-55591
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-55591
- OSV: https://osv.dev/vulnerability/CVE-2026-55591

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-55591/
Summaries are generated and may contain mistakes; the official description above is the record.