CVE-2025-68620: Signal K Server vulnerable to JWT Token Theft via WebSocket Enumeration and Unauthenticated Polling

Should you act?

Critical and remotely reachable

No known exploitation yet, but it is network-reachable without credentials. This signal is computed from CISA KEV, EPSS and CVSS data; it is not an editorial verdict.

• Not in CISA KEV, but CISA’s SSVC assessment records a public proof-of-concept, so attack code exists.
• EPSS 0.5%, percentile 45: FIRST’s model estimates a 0.5% chance of exploitation activity in the next 30 days, higher than 45% of all scored CVEs (low). EPSS is a probability, not a verdict.
• Remotely reachable with no login and no user interaction. If the vulnerable service is exposed to the internet, prioritize it.
• Only applies if your dependency tree includes signalk-server (npm) < 2.19.0, fixed in 2.19.0. Check your lockfile, including transitive dependencies.

What it is

Signal K Server is a server application that runs on a central hub in a boat. Versions prior to 2.19.0 expose two features that can be chained together to steal JWT authentication tokens without any prior authentication. The attack combines WebSocket-based request enumeration with unauthenticated polling of access request status. The first is Unauthenticated WebSocket Request Enumeration: When a WebSocket client connects to the SignalK stream endpoint with the serverevents=all query parameter, the server sends all cached server events including ACCESSREQUEST events that contain details about pending access requests. The startServerEvents function iterates over app.lastServerEvents and writes each cached event to any connected client without verifying authorization level. Since WebSocket connections are allowed for readonly users (which includes unauthenticated users when allowreadonly is true), attackers receive these events containing request IDs, client identifiers, descriptions, requested permissions, and IP addresses. The second is Unauthenticated Token Polling: The access request status endpoint at /signalk/v1/access/requests/:id returns the full state of an access request without requiring authentication. When an administrator approves a request, the response includes the issued JWT token in plaintext. The queryRequest function returns the complete request object including the token field, and the REST endpoint uses readonly authentication, allowing unauthenticated access. An attacker has two paths to exploit these vulnerabilities. Either the attacker creates their own access request (using the IP spoofing vulnerability to craft a convincing spoofed request), then polls their own request ID until an administrator approves it, receiving the JWT token; or the attacker passively monitors the WebSocket stream to discover request IDs from legitimate devices, then polls those IDs and steals the JWT tokens when administrators approve them, hijacking legitimate device credentials. Both paths require zero authentication and enable complete authentication bypass. Version 2.19.0 fixes the underlying issues.

From the GitHub advisory

SignalK Server exposes two features that can be chained together to steal JWT authentication tokens without any prior authentication. The attack combines WebSocket-based request enumeration with unauthenticated polling of access request status.

Unauthenticated WebSocket Request Enumeration: When a WebSocket client connects to the SignalK stream endpoint with the serverevents=all query parameter, the server sends all cached server events including ACCESSREQUEST events that contain details about pending access requests. The startServerEvents function iterates over app.lastServerEvents and writes each cached event to any connected client without verifying authorization level. Since WebSocket connections are allowed for readonly users (which includes unauthenticated users when allowreadonly is true), attackers receive these events containing request IDs, client identifiers, descriptions, requested permissions, and IP addresses.

Unauthenticated Token Polling: The access request status endpoint at /signalk/v1/access/requests/:id returns the full state of an access request without requiring authentication. When an administrator approves a request, the response includes the issued JWT token in plaintext. The queryRequest function returns the complete request object including the token field, and the REST endpoint uses readonly authentication, allowing unauthenticated access.

An attacker has two paths to exploit these vulnerabilities:

1. The attacker creates their own access request (using the IP spoofing vulnerability to craft a convincing spoofed request), then polls their own request ID until an administrator approves it, receiving the JWT token.

Weakness type: CWE-288.

Product: signalk-server (npm) · Assigned by: GitHub_M · Published: 2026-01-01

Affected and fixed versions

Severity scores

• Attack vector: network (remotely reachable)
• Attack complexity: low
• Privileges required: none (no login)
• User interaction: none
• Scope: unchanged

CVSS measures how bad a flaw is if exploited, not how likely exploitation is. Read it next to the exploitation data below.

Exploitation and urgency

• CISA KEV: not listed (no confirmed in-the-wild exploitation known to CISA).
• CISA SSVC assessment: exploitation poc, automatable yes, technical impact total.
• FIRST EPSS (model of 2026-10-21): 0.54% probability of exploitation activity in the next 30 days; percentile 45.

Timeline

• 2026-01-01 — CVE record published by GitHub_M
• 2026-01-02 — CVE record last updated
• 2026-01-02 — GitHub-reviewed advisory GHSA-fq56-hvg6-wvm5 published (critical)

Sources and references

Original sources first. Version and fix details should always be confirmed against the vendor or project advisory.

Vulnerability records

1. GitHub Advisory GHSA-fq56-hvg6-wvm5 github.com
2. CVE.org record CVE-2025-68620 cve.org
3. NVD entry CVE-2025-68620 nvd.nist.gov

Other references from the CVE record and advisory

1. github.com github.com
2. github.com github.com
3. github.com github.com

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