Signal K Server has Unauthenticated State Pollution leading to Remote Code Execution (RCE)

Exploitation

No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.

CVSS

9.6 · CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:H/I:H/A:H

EPSS

• CVE-2025-66398: 19.85% estimated exploitation activity in the next 30 days; percentile 97.42 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.

As published by the source; long descriptions are shortened.

Summary An unauthenticated attacker can pollute the internal state (restoreFilePath) of the server via the /skServer/validateBackup endpoint. This allows the attacker to hijack the administrator's "Restore" functionality to overwrite critical server configuration files (e.g., security.json, package.json), leading to account takeover and Remote Code Execution (RCE). Details The vulnerability is caused by the use of a module-level global variable restoreFilePath in src/serverroutes.ts, which is shared across all requests. Vulnerable Code Analysis: 1. Global State: restoreFilePath is defined at the top level of the module. 2. Unauthenticated State Pollution: The /skServer/validateBackup endpoint updates this variable. Crucially, this endpoint lacks authentication middleware, allowing any user to access it. 3. Restore Hijacking: The /skServer/restore endpoint uses the polluted restoreFilePath to perform the restoration. Exploit Chain: 1. Pollution: Attacker uploads a malicious zip file…

Published by the source

2 Jan 2026, 15:11 UTC

Last modified by the source

27 Apr 2026, 11:36 UTC

Source last checked

26 Oct 2026, 12:51 UTC

1. Revision 3 · amended · 26 Oct 2026

   Amended from ghsa record GHSA-w3x5-7c4c-66p9

2. Revision 2 · amended · 24 Oct 2026

   Amended from osv record GHSA-w3x5-7c4c-66p9

3. Revision 1 · created · 23 Oct 2026

   Published from ghsa record GHSA-w3x5-7c4c-66p9

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# Patch Next advisory brief: CVE-2025-66398

Advisory: Signal K Server has Unauthenticated State Pollution leading to Remote Code Execution (RCE)
IDs: CVE-2025-66398, GHSA-w3x5-7c4c-66p9
Record: https://patchnext.com/advisories/cve-2025-66398 (revision 3, source checked 26 Oct 2026, 12:51 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: Critical (CVSS 9.6)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: signalk-server 2.19.0. A vendor fix does not mean a deployment is fixed.

## Affected components
- npm signalk-server: affected < 2.19.0; fixed in 2.19.0

## Suggested inspection (read-only)
- `npm ls signalk-server --all`: lists every installed copy and version, including transitive ones. Run in the project root after `npm ci`.

## Supported action
Upgrade each affected component to a fixed version on its release line. For a transitive dependency, upgrade the parent package or add an override or constraint, then regenerate the lockfile. Redeploy every environment that ran an affected version.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on signalk-server.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://github.com/advisories/GHSA-w3x5-7c4c-66p9 (GitHub-reviewed advisory GHSA-w3x5-7c4c-66p9 lists affected ranges: npm signalk-server >=0 <2.19.0)
- Verified: https://osv.dev/vulnerability/GHSA-w3x5-7c4c-66p9 (OSV record GHSA-w3x5-7c4c-66p9 lists affected ranges: npm signalk-server >=0 <2.19.0 (fixed))

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