CVE-2026-55430

Vulnerability Description

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.

CVSS Score

Affected Products

Related Weaknesses (CWE)

References

• https://github.com/coder/coder/pull/26204Issue TrackingPatch
• https://github.com/coder/coder/releases/tag/v2.29.17Release Notes
• https://github.com/coder/coder/releases/tag/v2.32.7Release Notes
• https://github.com/coder/coder/releases/tag/v2.33.8Release Notes
• https://github.com/coder/coder/releases/tag/v2.34.2Release Notes
• https://github.com/coder/coder/security/advisories/GHSA-5g4w-3vw9-478wPatchVendor Advisory