# CVE-2026-34083: signalk-server: OAuth Authorization Code Theft via Unvalidated Host Header in OIDC Flow

> Attackers can steal OAuth authorization codes by spoofing the Host header, leading to session hijacking in Signal K Server deployments.

- **Severity:** Medium 6.1 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** A user has to click or open something
- **Fix available:** Yes
- **Published:** 2 Apr 2026
- **Updated:** 2 Apr 2026
- **Also known as:** GHSA-cxj8-ggf2-p57c

## What is CVE-2026-34083?

CVE-2026-34083 is a medium-severity vulnerability in signalk-server, published on 2 Apr 2026. An attacker can exploit it over the internet without logging in, and only if a user opens a file or follows a link.

### Official description

Signal K Server is a server application that runs on a central hub in a boat. Prior to version 2.24.0, 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 redirect_uri. Because the redirectUri configuration is silently unset by default, an attacker can 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. This issue has been patched in version 2.24.0.

Weakness: CWE-601 (URL Redirection to Untrusted Site), CWE-346 (Origin Validation Error)

## Which versions are affected by CVE-2026-34083?

2 open source packages ship an affected version, including signalk-server. It affects 1 product.


| Package | Ecosystem | Affected | Fixed in |
| --- | --- | --- | --- |
| `signalk-server` | npm | From 2.20.0 | 2.24.0 |
| `signalk-server` | npm | From 2.20.0 | 2.24.0 |

Products: Signalk Signal K Server.

## How do I fix CVE-2026-34083?

Upgrade signalk-server to 2.24.0 or later.

## Is CVE-2026-34083 being exploited?

It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-34083 exists.

## Other vulnerabilities in signalk-server

- [CVE-2026-23515](https://insights.sbomify.com/CVE-2026-23515/): RCE - Command Injection in Signal K set-system-time plugin (critical 10.0)
- [CVE-2025-66398](https://insights.sbomify.com/CVE-2025-66398/): Signal K Server has Unauthenticated State Pollution leading to Remote Code Execution (RCE) (critical 9.7)
- [CVE-2026-33950](https://insights.sbomify.com/CVE-2026-33950/): signalk-server: Privilege Escalation by Admin Role Injection via /enableSecurity (critical 9.4)
- [CVE-2025-68620](https://insights.sbomify.com/CVE-2025-68620/): Signal K Server vulnerable to JWT Token Theft via WebSocket Enumeration and Unauthenticated Polling (critical 9.1)
- [CVE-2026-41893](https://insights.sbomify.com/CVE-2026-41893/): Signal K Server's WebSocket Login Endpoint Lacks Rate Limiting (Credential Brute-Force) (high 8.7)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-34083 and fix it if it is affected.

What it is: CVE-2026-34083 is a medium-severity vulnerability in signalk-server, published on 2 Apr 2026. An attacker can exploit it over the internet without logging in, and only if a user opens a file or follows a link.
Exploitation: It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-34083 exists.

Affected packages and fixed versions:
- signalk-server (npm): affected from 2.20.0; fixed in 2.24.0
- signalk-server (npm): affected from 2.20.0; fixed in 2.24.0

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-34083/ (Markdown: https://insights.sbomify.com/CVE-2026-34083/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-34083
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-34083
- OSV: https://osv.dev/vulnerability/CVE-2026-34083

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-34083/
Summaries are generated and may contain mistakes; the official description above is the record.