{"id":"CVE-2026-81315","aliases":["EEF-CVE-2026-81315","GHSA-c92r-f3rr-q49h"],"url":"https://o3.security/vulnerability/CVE-2026-81315","summary":"MCP DNS-rebinding origin check in AshAi is bypassed by a spoofed X-Forwarded-Proto header","details":"Origin Validation Error vulnerability in ash-project ash_ai allows a malicious web page to bypass the MCP server's DNS-rebinding protection and issue cross-site requests to a user's local MCP server with that user's actor.\n\nIn AshAi.Mcp.Server, with the default allowed_origins: nil, origin_allowed?/3 accepts an origin when uri.host == conn.host and the forwarded scheme is https. Both values are attacker-controlled: conn.host comes from the Host header and the scheme is read from the raw x-forwarded-proto header with no trusted-proxy check. Under DNS rebinding the browser sends the attacker's origin and a matching host, and page JavaScript may set X-Forwarded-Proto: https, so the check passes with no TLS or proxy involved. The fix trusts only localhost origins by default; other origins require an explicit allowed_origins allowlist.\n\nThis issue affects ash_ai: from 0.8.0 before 1.0.0.","published":"2026-08-31T00:57:55.910Z","modified":"2026-09-01T03:46:14.079613865Z","cvss":null,"epss":null,"cisaKev":null,"exploitsKnown":null,"affectedPackages":[],"fix":{"url":"https://github.com/ash-project/ash_ai/commit/28af68d73134df0b8fb3aa6ab03e8fd795b07c21","label":"ash-project/ash_ai@28af68d"},"references":[{"type":"WEB","url":"https://cna.erlef.org/cves/CVE-2026-81315.html"},{"type":"WEB","url":"https://github.com"},{"type":"WEB","url":"https://osv.dev/vulnerability/EEF-CVE-2026-81315"},{"type":"WEB","url":"https://repo.hex.pm"},{"type":"ADVISORY","url":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/81xxx/CVE-2026-81315.json"},{"type":"ADVISORY","url":"https://github.com/ash-project/ash_ai/security/advisories/GHSA-c92r-f3rr-q49h"},{"type":"ADVISORY","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-81315"},{"type":"FIX","url":"https://github.com/ash-project/ash_ai/commit/28af68d73134df0b8fb3aa6ab03e8fd795b07c21"},{"type":"PACKAGE","url":"https://github.com/ash-project/ash_ai"}],"provenance":{"sources":["OSV.dev","FIRST.org (EPSS)"],"lastVerified":"2026-09-01T03:46:14.079613865Z"}}