{"id":"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.","aliases":["EEF-CVE-2026-81315","GHSA-c92r-f3rr-q49h"],"modified":"2026-09-01T03:46:14.079613865Z","published":"2026-08-31T00:57:55.910Z","database_specific":{"cna_assigner":"EEF","cwe_ids":["CWE-346"],"osv_generated_from":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/81xxx/CVE-2026-81315.json","unresolved_ranges":[{"extracted_events":[{"introduced":"c94f0b17fbe252f68755ba512678586164ba6139"},{"fixed":"28af68d73134df0b8fb3aa6ab03e8fd795b07c21"}],"source":"AFFECTED_FIELD"}]},"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"}],"affected":[{"ranges":[{"type":"GIT","repo":"https://github.com/ash-project/ash_ai","events":[{"introduced":"9dc782541629a80df5f13876b40c78ab882214a1"},{"fixed":"f72b14744996e71df6d73480d617d963f340597b"},{"fixed":"28af68d73134df0b8fb3aa6ab03e8fd795b07c21"}],"database_specific":{"extracted_events":[{"introduced":"0.8.0"},{"fixed":"1.0.0"}],"source":["DESCRIPTION","REFERENCES"]}}],"versions":["v0.8.2","v0.8.1","v0.8.0"],"database_specific":{"source":"https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-81315.json"}}],"schema_version":"1.9.0","severity":[{"type":"CVSS_V4","score":"CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:A/VC:H/VI:H/VA:N/SC:N/SI:N/SA:N"}]}