{"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,"slug":"CVE-2026-55430","body":"## Overview\n\n### 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> **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!\n\n## Affected packages\n\n- `github.com/coder/coder/v2 >= 2.34.0, < 2.34.2`\n- `github.com/coder/coder/v2 >= 2.33.0, < 2.33.8`\n- `github.com/coder/coder/v2 >= 2.30.0, < 2.32.7`\n- `github.com/coder/coder/v2 < 2.29.17`\n\n## Remediation\n\nUpgrade to a patched release:\n\n- `github.com/coder/coder/v2 2.34.2`\n- `github.com/coder/coder/v2 2.33.8`\n- `github.com/coder/coder/v2 2.32.7`\n- `github.com/coder/coder/v2 2.29.17`","depth":"sunlit","depthScore":32,"depthScoreParts":{"impact":31.9,"likelihood":0,"exploitation":0,"ransomware":0},"changes":[]}