Coder's subdomain workspace app routing trusts unauthenticated X-Forwarded-Host header, enabling cross-app data access

Summary

Coder allows organizations to provision remote development environments via Terraform. Prior to versions 2.29.7, 2.32.7, 2.33.8, and 2.34.2, 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. 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`. The fix in versions 2.29.7, 2.32.7, 2.33.8, and 2.34.2 trusts `X-Forwarded-Host` only from configured trusted proxies and otherwise resolves the routing host from the verified request host. As a workaround, place an upstream reverse proxy that strips or overwrites `X-Forwarded-Host` on untrusted requests.

Timeline

1. Jul 8, 2026, 12:03 AM UTCCVE published
2. Jul 8, 2026, 4:57 PM UTCCISA SSVC assessment

   Exploitation: none · Automatable: no · Technical impact: partial

3. Jul 8, 2026, 5:10 PM UTCRecord last updated

Affected versions

• coder coder

  From 2.34.0 · fixed in 2.34.2; From 2.33.0 · fixed in 2.33.8; From 2.30.0 · fixed in 2.32.7; fixed in 2.29.17

• github.com/coder/coder/v2Go

  From 2.34.0 · fixed in 2.34.2

• github.com/coder/coder/v2Go

  From 2.33.0 · fixed in 2.33.8

• github.com/coder/coder/v2Go

  From 2.30.0 · fixed in 2.32.7

• github.com/coder/coder/v2Go

  fixed in 2.29.17

• github.com/coder/coderGo

  All versions

• github.com/coder/coder/v2Go

  fixed in 2.29.17; From 2.30.0 · fixed in 2.32.7; From 2.33.0 · fixed in 2.33.8; From 2.34.0 · fixed in 2.34.2

References 6