{"id":"GHSA-5g4w-3vw9-478w","summary":"Coder's subdomain workspace app routing trusts unauthenticated X-Forwarded-Host header, enabling cross-app data access","details":"### Summary\n\nThe 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.\n\n\u003e **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`.\n\n### Impact\n\nApp 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`.\n\n### Patches\n\nThe fix trusts `X-Forwarded-Host` only from configured trusted proxies and otherwise resolves the routing host from the verified request host.\n\nThe fix was backported to all supported release lines:\n\n| Release line | Patched version |\n|---|---|\n| 2.34 | [v2.34.2](https://github.com/coder/coder/releases/tag/v2.34.2) |\n| 2.33 | [v2.33.8](https://github.com/coder/coder/releases/tag/v2.33.8) |\n| 2.32 | [v2.32.7](https://github.com/coder/coder/releases/tag/v2.32.7) |\n| 2.29 (ESR) | [v2.29.17](https://github.com/coder/coder/releases/tag/v2.29.17) |\n\n### Workarounds\n\nPlace an upstream reverse proxy that strips or overwrites `X-Forwarded-Host` on untrusted requests.\n\n### Resources\n\n- Fix: #26204\n\n### Credits\n\nCoder would like to thank Anthropic's Security Team (ANT-2026-22435) for independently disclosing this issue!","aliases":["CVE-2026-55430","GO-2026-5917"],"modified":"2026-07-07T20:41:31.259914774Z","published":"2026-07-06T21:05:31Z","database_specific":{"nvd_published_at":null,"cwe_ids":["CWE-345","CWE-441"],"severity":"MODERATE","github_reviewed":true,"github_reviewed_at":"2026-07-06T21:05:31Z"},"references":[{"type":"WEB","url":"https://github.com/coder/coder/security/advisories/GHSA-5g4w-3vw9-478w"},{"type":"WEB","url":"https://github.com/coder/coder/pull/26204"},{"type":"PACKAGE","url":"https://github.com/coder/coder"}],"affected":[{"package":{"name":"github.com/coder/coder/v2","ecosystem":"Go","purl":"pkg:golang/github.com/coder/coder/v2"},"ranges":[{"type":"SEMVER","events":[{"introduced":"2.34.0"},{"fixed":"2.34.2"}]}],"database_specific":{"source":"https://github.com/github/advisory-database/blob/main/advisories/github-reviewed/2026/07/GHSA-5g4w-3vw9-478w/GHSA-5g4w-3vw9-478w.json"}},{"package":{"name":"github.com/coder/coder/v2","ecosystem":"Go","purl":"pkg:golang/github.com/coder/coder/v2"},"ranges":[{"type":"SEMVER","events":[{"introduced":"2.33.0"},{"fixed":"2.33.8"}]}],"database_specific":{"source":"https://github.com/github/advisory-database/blob/main/advisories/github-reviewed/2026/07/GHSA-5g4w-3vw9-478w/GHSA-5g4w-3vw9-478w.json"}},{"package":{"name":"github.com/coder/coder/v2","ecosystem":"Go","purl":"pkg:golang/github.com/coder/coder/v2"},"ranges":[{"type":"SEMVER","events":[{"introduced":"2.30.0"},{"fixed":"2.32.7"}]}],"database_specific":{"source":"https://github.com/github/advisory-database/blob/main/advisories/github-reviewed/2026/07/GHSA-5g4w-3vw9-478w/GHSA-5g4w-3vw9-478w.json"}},{"package":{"name":"github.com/coder/coder/v2","ecosystem":"Go","purl":"pkg:golang/github.com/coder/coder/v2"},"ranges":[{"type":"SEMVER","events":[{"introduced":"0"},{"fixed":"2.29.17"}]}],"database_specific":{"source":"https://github.com/github/advisory-database/blob/main/advisories/github-reviewed/2026/07/GHSA-5g4w-3vw9-478w/GHSA-5g4w-3vw9-478w.json"}}],"schema_version":"1.9.0","severity":[{"type":"CVSS_V3","score":"CVSS:3.1/AV:N/AC:H/PR:L/UI:R/S:C/C:H/I:N/A:N"}]}