CVE-2026-55430
Coder's subdomain workspace app routing trusts unauthenticated X-Forwarded-Host header, enabling cross-app data access
Impact
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.
Affected packages
| Ecosystem | Package | Affected | Fixed in |
|---|---|---|---|
| go | github.com/coder/coder/v2 | >= 2.34.0, < 2.34.2 | 2.34.2 |
Affected products
| Vendor | Product | Affected versions |
|---|---|---|
| Coder | Coder | before 2.29.17 from 2.30.0 before 2.32.7 from 2.33.0 before 2.33.8 from 2.34.0 before 2.34.2 |
Weakness classification
References
- NVD record
- CVE.org record
- GitHub advisory
- https://github.com/advisories/GHSA-5g4w-3vw9-478w
- https://github.com/coder/coder/security/advisories/GHSA-5g4w-3vw9-478w
- https://github.com/coder/coder/pull/26204
- https://github.com/coder/coder/releases/tag/v2.29.17
- https://github.com/coder/coder/releases/tag/v2.32.7
- https://github.com/coder/coder/releases/tag/v2.33.8
- https://github.com/coder/coder/releases/tag/v2.34.2