CVE-2026-34083 is a medium-severity open redirect vulnerability in signalk-server (npm), affecting versions >= 2.20.0, < 2.24.0. It is fixed in 2.24.0.
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 fallback In types.ts:30, redirectUri is declared as optional The defaults in types.ts:175-185 do not include a redirectUri: never checks or warns about a missing redirectUri. This means a fully "valid" OIDC configuration can exist without redirectUri, silently activating the vulnerable fallback path. Factor 2: Unsafe Host header usage in two locations Location 1, Login handler in oidc-auth.ts:278-282: This redirectUri flows into createAuthState() → buildAuthorizationUrl() → OIDC provider's redirecturi parameter. The OIDC provider will then send the authorization code to whatever domain was injected. Location 2, Logout handler in oidc-auth.ts:513-515: This constructs the postlogoutredirecturi sent to the OIDC provider's endsessionendpoint, allowing an attacker to redirect the user to an attacker controlled domain after logout. Official Documentation Enables the Attack SignalK's own security documentation at docs/security.md:222-228 provides the recommended nginx reverse proxy configuration: The proxysetheader Host $host; directive forwards the client-supplied Host header to the backend unmodified. Without this directive, nginx would replace the Host header with the upstream address (localhost:3000), which would neutralize the injection. Administrators who follow the official documentation are directly enabling this vulnerability behind their reverse proxy. Proof of Concept Tested against SignalK Server v2.23.0 in Docker with OIDC enabled . Step 1, Send login request with injected Host header: $response = Invoke-WebRequest -Uri "http://localhost:3000/signalk/v1/auth/oidc/login" -Headers @{"Host"="evil.com"} -MaximumRedirection 0 -ErrorAction SilentlyContinue -UseBasicParsing Step 2: Decode and print the injected redirect URL [uri]::UnescapeDataString($response.Headers.Location) <img width="1259" height="211" alt="Screenshot 2026-03-25 171251" src="https://github.com/user-attachments/assets/6e4a9655-639e-48c2-a7f0-06e17ad471ff" /> Impact Authorization Code Theft: The OIDC provider sends the OAuth authorization code to the attacker's domain instead of the legitimate server. Session Hijack: The attacker can exchange the stolen code for tokens and create a session as the victim user. Logout Redirect Hijack: The logout handler has the same pattern, allowing post-logout redirection to an attacker domain (phishing opportunity).
Untrusted input controls a URL used for redirection, which can forward users to attacker-controlled sites. Typical impact: phishing and credential harvesting via a trusted domain.
CVE-2026-34083 has a CVSS score of 6.1 (Medium). The vector is network-reachable, no privileges required, and user interaction required. A CVSS score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether this affects your application depends on whether the vulnerable code is present and reachable in your environment.
A fixed version is available (2.24.0). Upgrading removes the vulnerable code path.
npm
signalk-server (>= 2.20.0, < 2.24.0)signalk-server → 2.24.0 (npm)Severity tells you how bad this could be in the worst case. It does not tell you whether you are exposed. Exploitability and impact are functions of runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A vulnerable package can sit in your dependency tree and never run.
Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter instead of chasing every advisory.
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Upgrade signalk-server to 2.24.0 or later to resolve this vulnerability.
Kodem Kai can prioritize this vulnerability in your dependency tree and generate a fix recommendation.
CVE-2026-34083 is a medium-severity open redirect vulnerability in signalk-server (npm), affecting versions >= 2.20.0, < 2.24.0. It is fixed in 2.24.0. Untrusted input controls a URL used for redirection, which can forward users to attacker-controlled sites.
CVE-2026-34083 has a CVSS score of 6.1 (Medium). This score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether it represents real risk in your environment depends on whether the vulnerable code is present and reachable.
signalk-server (npm) versions >= 2.20.0, < 2.24.0 is affected.
Yes. CVE-2026-34083 is fixed in 2.24.0. Upgrade to this version or later.
Whether CVE-2026-34083 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
Upgrade signalk-server to 2.24.0 or later.