{"id":"CVE-2026-55430","aliases":["GHSA-5g4w-3vw9-478w","GO-2026-5917"],"url":"https://o3.security/vulnerability/CVE-2026-55430","summary":"Coder's subdomain workspace app routing trusts unauthenticated X-Forwarded-Host header, enabling cross-app data access","details":"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.","published":"2026-07-08T00:03:29.728Z","modified":"2026-08-12T03:51:09.431328823Z","cvss":{"score":5.8,"severity":"MEDIUM","vector":"CVSS:3.1/AV:N/AC:H/PR:L/UI:R/S:C/C:H/I:N/A:N"},"epss":{"score":0.00208,"percentile":0.10963,"asOf":"2026-09-08"},"cisaKev":null,"exploitsKnown":0,"affectedPackages":[{"ecosystem":"Go","name":"github.com/coder/coder/v2","fixedVersion":"2.34.2"},{"ecosystem":"Go","name":"github.com/coder/coder/v2","fixedVersion":"2.33.8"},{"ecosystem":"Go","name":"github.com/coder/coder/v2","fixedVersion":"2.32.7"},{"ecosystem":"Go","name":"github.com/coder/coder/v2","fixedVersion":"2.29.17"}],"fix":{"url":"https://github.com/coder/coder/pull/26204","label":"coder/coder#26204"},"references":[{"type":"WEB","url":"https://github.com/coder/coder/releases/tag/v2.29.17"},{"type":"WEB","url":"https://github.com/coder/coder/releases/tag/v2.32.7"},{"type":"WEB","url":"https://github.com/coder/coder/releases/tag/v2.33.8"},{"type":"WEB","url":"https://github.com/coder/coder/releases/tag/v2.34.2"},{"type":"ADVISORY","url":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/55xxx/CVE-2026-55430.json"},{"type":"ADVISORY","url":"https://github.com/coder/coder/security/advisories/GHSA-5g4w-3vw9-478w"},{"type":"ADVISORY","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-55430"},{"type":"FIX","url":"https://github.com/coder/coder/pull/26204"}],"provenance":{"sources":["OSV.dev","FIRST.org (EPSS)"],"lastVerified":"2026-08-12T03:51:09.431328823Z"}}