---
id: CVE-2026-55430
aliases:
  - GHSA-5g4w-3vw9-478w
title: >-
  Coder's subdomain workspace app routing trusts unauthenticated
  X-Forwarded-Host header, enabling cross-app data access
summary: >-
  Coder's subdomain workspace app routing trusts unauthenticated
  X-Forwarded-Host header, enabling cross-app data access
severity: medium
cvss: 5.8
cwe:
  - CWE-345
  - CWE-441
vendor: coder
product: github.com/coder/coder/v2
ecosystem: go
affected:
  - 'github.com/coder/coder/v2 >= 2.34.0, < 2.34.2'
  - 'github.com/coder/coder/v2 >= 2.33.0, < 2.33.8'
  - 'github.com/coder/coder/v2 >= 2.30.0, < 2.32.7'
  - github.com/coder/coder/v2 < 2.29.17
patched:
  - github.com/coder/coder/v2 2.34.2
  - github.com/coder/coder/v2 2.33.8
  - github.com/coder/coder/v2 2.32.7
  - github.com/coder/coder/v2 2.29.17
published: '2026-07-06'
updated: '2026-07-06'
source: GHSA
sourceUrl: 'https://github.com/advisories/GHSA-5g4w-3vw9-478w'
references:
  - url: 'https://github.com/coder/coder/security/advisories/GHSA-5g4w-3vw9-478w'
  - url: 'https://github.com/coder/coder/pull/26204'
  - url: 'https://github.com/advisories/GHSA-5g4w-3vw9-478w'
tags:
  - ghsa
  - go
ingestedAt: '2026-07-06T21:45:52.963Z'
epss: 0.00208
epssPercentile: 0.11267
---

## Overview

### Summary

The workspace app proxy resolves the target app from `httpapi.RequestHost()` which prefers the `X-Forwarded-Host` header over the real `Host` header. No middleware strips `X-Forwarded-Host` before routing and the header is not browser-forbidden so client-side JavaScript can set it on `fetch()` calls.

> **Note:** Practical exploitation requires subdomain app routing (wildcard hostname) enabled, a victim who visits the attacker's shared app and a deployment whose upstream proxy does not strip `X-Forwarded-Host`.

### Impact

App session cookies are scoped to the wildcard parent domain so the browser attaches them to any app subdomain. An attacker who controls a shared workspace app can serve JavaScript that sends same-site requests with a forged `X-Forwarded-Host` pointing at a victim's private app. The server routes by the attacker-controlled header but authorizes with the victim's cookie which lets the attacker read the victim's private app responses. Subdomain app routing must be enabled and no upstream proxy may strip `X-Forwarded-Host`.

### Patches

The fix trusts `X-Forwarded-Host` only from configured trusted proxies and otherwise resolves the routing host from the verified request host.

The fix was backported to all supported release lines:

| Release line | Patched version |
|---|---|
| 2.34 | [v2.34.2](https://github.com/coder/coder/releases/tag/v2.34.2) |
| 2.33 | [v2.33.8](https://github.com/coder/coder/releases/tag/v2.33.8) |
| 2.32 | [v2.32.7](https://github.com/coder/coder/releases/tag/v2.32.7) |
| 2.29 (ESR) | [v2.29.17](https://github.com/coder/coder/releases/tag/v2.29.17) |

### Workarounds

Place an upstream reverse proxy that strips or overwrites `X-Forwarded-Host` on untrusted requests.

### Resources

- Fix: #26204

### Credits

Coder would like to thank Anthropic's Security Team (ANT-2026-22435) for independently disclosing this issue!

## Affected packages

- `github.com/coder/coder/v2 >= 2.34.0, < 2.34.2`
- `github.com/coder/coder/v2 >= 2.33.0, < 2.33.8`
- `github.com/coder/coder/v2 >= 2.30.0, < 2.32.7`
- `github.com/coder/coder/v2 < 2.29.17`

## Remediation

Upgrade to a patched release:

- `github.com/coder/coder/v2 2.34.2`
- `github.com/coder/coder/v2 2.33.8`
- `github.com/coder/coder/v2 2.32.7`
- `github.com/coder/coder/v2 2.29.17`