CVE-2026-39320: Signal K Server has an Unauthenticated Regular Expression Denial of Service (ReDoS) via WebSocket Subscription Paths

CVE-2026-39320 · Severity: high · CVSS 7.5 · Published 2026-04-21

Signal K Server is an open-source marine data platform that manages real-time sensor data via WebSocket connections. An attacker can send a specially crafted WebSocket subscription request without authentication, causing the server's CPU to spike to 100% and become completely unresponsive to all requests. This results in total service unavailability and affects any vessel, sensor network, or marine system relying on Signal K for navigation and monitoring data.

Technologies: signalk-server (npm), Signalk Signal K Server. Vendors: npm, Signalk.

Quick answers

Is CVE-2026-39320 exploited in the wild?
No. Junglewise Threat Intelligence has no report of CVE-2026-39320 being exploited in the wild.
How severe is CVE-2026-39320?
High severity, with a CVSS score of 7.5, published 21 April 2026.
Which products and versions are affected?
signalk-server (npm) < 2.25.0, SEMVER:introduced=0,fixed=2.25.0.
Is there a fix for CVE-2026-39320?
Yes. signalk-server (npm): upgrade to 2.25.0 or later. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.
How is CVE-2026-39320 attacked?
It is attacked over the network.
Am I affected by CVE-2026-39320?
Check whether you run signalk-server (npm) or Signalk Signal K Server at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

How to fix

  • signalk-server (npm): upgrade to 2.25.0 or later
    npm install signalk-server@2.25.0

Technical details

This is a Regular Expression Denial of Service (ReDoS) vulnerability in the subscription manager's contextMatcher() and pathMatcher() functions in subscriptionmanager.ts. The vulnerable code converts user-supplied wildcard strings directly into regular expressions, escaping only dots and asterisks but leaving other regex metacharacters (+, (, ), ?, [, ]) unescaped. An unauthenticated attacker can inject nested quantifiers (e.g., ([a-z0-9:-]+)+!) via a WebSocket subscription's context parameter. When the regex engine attempts to match this pattern against legitimate long identifiers (like vessels.urn:mrn:signalk:uuid:...), it triggers catastrophic backtracking with billions of evaluation attempts. Since Node.js uses a single-threaded event loop, this indefinitely locks the thread. The attack requires only network access to the WebSocket endpoint and no authentication. Signal K Server version 2.25.0 and later contain a fix.

Affected products

  • Signal K Server All versions prior to 2.25.0

Identifiers

  • CVE-2026-39320
  • GHSA-7gcj-phff-2884

Timeline

  • 2026-04-21: disclosed

References

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