Signal K Server: OAuth Authorization Code Theft via Unvalidated Host Header in OIDC Flow

Exploitation

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

CVSS

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

EPSS

• CVE-2026-34083: 0.12% estimated exploitation activity in the next 30 days; percentile 1.63 (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 SignalK Server contains a code-level vulnerability in its OIDC login and logout handlers where the unvalidated HTTP Host header is used to construct the OAuth2 redirecturi. Because the redirectUri configuration is silently unset by default, an attacker spoof the Host header to steal OAuth authorization codes and hijack user sessions in realistic deployments as The OIDC provider will then send the authorization code to whatever domain was injected. The OIDC specification requires redirecturi to be pre-registered and not derived from untrusted input. Constructing it from the Host header violates this requirement and introduces a trust boundary break. This risk is actively amplified by SignalK's official documentation, which instructs administrators to deploy an Nginx configuration that forwards the vulnerable Host header, exposing production environments. Vulnerability Root Cause Two factors combine to create this vulnerability: Factor 1: redirectUri is optional with an unsafe…

Published by the source

3 Apr 2026, 21:43 UTC

Last modified by the source

3 Apr 2026, 21:56 UTC

Source last checked

26 Oct 2026, 12:47 UTC

1. Revision 2 · amended · 26 Oct 2026

   Amended from ghsa record GHSA-cxj8-ggf2-p57c

2. Revision 1 · created · 24 Oct 2026

   Published from osv record GHSA-cxj8-ggf2-p57c

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# Patch Next advisory brief: CVE-2026-34083

Advisory: Signal K Server: OAuth Authorization Code Theft via Unvalidated Host Header in OIDC Flow
IDs: CVE-2026-34083, GHSA-cxj8-ggf2-p57c
Record: https://patchnext.com/advisories/cve-2026-34083 (revision 2, source checked 26 Oct 2026, 12:47 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: Medium (CVSS 6.1)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: signalk-server 2.24.0. A vendor fix does not mean a deployment is fixed.

## Affected components
- npm signalk-server: affected >= 2.20.0, < 2.24.0; fixed in 2.24.0

## 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://osv.dev/vulnerability/GHSA-cxj8-ggf2-p57c (OSV record GHSA-cxj8-ggf2-p57c lists affected ranges: npm signalk-server >=2.20.0 <2.24.0 (fixed))
- Verified: https://github.com/advisories/GHSA-cxj8-ggf2-p57c (GitHub-reviewed advisory GHSA-cxj8-ggf2-p57c lists affected ranges: npm signalk-server >=2.20.0 <2.24.0)

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