{"id":"CVE-2026-81315","state":"PUBLISHED","title":"MCP DNS-rebinding origin check in AshAi is bypassed by a spoofed X-Forwarded-Proto header","description":"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.","publishedAt":"2026-08-31T00:57:55.910Z","updatedAt":"2026-08-31T16:02:38.700Z","severity":{"score":7.4,"label":"High","version":"4.0","vector":"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","source":"EEF"},"assigner":"EEF","products":["ash-project ash_ai"],"affected":[{"vendor":"ash-project","product":"ash_ai","packageName":"ash_ai","packageURL":"pkg:hex/ash_ai","defaultStatus":"unaffected","versions":[{"version":"0.8.0","status":"affected","lessThan":"1.0.0","versionType":"semver"}],"collectionURL":"https://repo.hex.pm","cpes":["cpe:2.3:a:ash-project:ash_ai:*:*:*:*:*:*:*:*"],"modules":["'Elixir.AshAi.Mcp.Server'"],"programFiles":["lib/ash_ai/mcp/server.ex"],"programRoutines":[{"name":"'Elixir.AshAi.Mcp.Server':check_origin/2"},{"name":"'Elixir.AshAi.Mcp.Server':origin_allowed?/3"}],"repo":"https://github.com/ash-project/ash_ai"},{"vendor":"ash-project","product":"ash_ai","packageName":"ash-project/ash_ai","packageURL":"pkg:github/ash-project/ash_ai","defaultStatus":"unaffected","versions":[{"version":"c94f0b17fbe252f68755ba512678586164ba6139","status":"affected","lessThan":"28af68d73134df0b8fb3aa6ab03e8fd795b07c21","versionType":"git"}],"collectionURL":"https://github.com","cpes":["cpe:2.3:a:ash-project:ash_ai:*:*:*:*:*:*:*:*"],"modules":["'Elixir.AshAi.Mcp.Server'"],"programFiles":["lib/ash_ai/mcp/server.ex"],"programRoutines":[{"name":"'Elixir.AshAi.Mcp.Server':check_origin/2"},{"name":"'Elixir.AshAi.Mcp.Server':origin_allowed?/3"}],"repo":"https://github.com/ash-project/ash_ai"}],"references":["https://github.com/ash-project/ash_ai/security/advisories/GHSA-c92r-f3rr-q49h","https://cna.erlef.org/cves/CVE-2026-81315.html","https://osv.dev/vulnerability/EEF-CVE-2026-81315","https://github.com/ash-project/ash_ai/commit/28af68d73134df0b8fb3aa6ab03e8fd795b07c21"],"weaknesses":["CWE-346"],"ingestedAt":"2026-10-29T20:13:15.269Z","source":{"repository":"CVEProject/cvelistV5","path":"cves/2026/81xxx/CVE-2026-81315.json","commit":"556c9d3a8cd17e218bb8e452ba7cd619a384ff47"},"raw":{"dataType":"CVE_RECORD","dataVersion":"5.2","cveMetadata":{"cveId":"CVE-2026-81315","state":"PUBLISHED","datePublished":"2026-08-31T00:57:55.910Z","dateUpdated":"2026-08-31T16:02:38.700Z","assignerShortName":"EEF","assignerOrgId":"6b3ad84c-e1a6-4bf7-a703-f496b71e49db","dateReserved":"2026-08-30T20:00:01.860Z"},"containers":{"cna":{"title":"MCP DNS-rebinding origin check in AshAi is bypassed by a spoofed X-Forwarded-Proto header","descriptions":[{"lang":"en","value":"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."}],"affected":[{"vendor":"ash-project","product":"ash_ai","packageName":"ash_ai","packageURL":"pkg:hex/ash_ai","defaultStatus":"unaffected","versions":[{"version":"0.8.0","status":"affected","lessThan":"1.0.0","versionType":"semver"}],"collectionURL":"https://repo.hex.pm","cpes":["cpe:2.3:a:ash-project:ash_ai:*:*:*:*:*:*:*:*"],"modules":["'Elixir.AshAi.Mcp.Server'"],"programFiles":["lib/ash_ai/mcp/server.ex"],"programRoutines":[{"name":"'Elixir.AshAi.Mcp.Server':check_origin/2"},{"name":"'Elixir.AshAi.Mcp.Server':origin_allowed?/3"}],"repo":"https://github.com/ash-project/ash_ai"},{"vendor":"ash-project","product":"ash_ai","packageName":"ash-project/ash_ai","packageURL":"pkg:github/ash-project/ash_ai","defaultStatus":"unaffected","versions":[{"version":"c94f0b17fbe252f68755ba512678586164ba6139","status":"affected","lessThan":"28af68d73134df0b8fb3aa6ab03e8fd795b07c21","versionType":"git"}],"collectionURL":"https://github.com","cpes":["cpe:2.3:a:ash-project:ash_ai:*:*:*:*:*:*:*:*"],"modules":["'Elixir.AshAi.Mcp.Server'"],"programFiles":["lib/ash_ai/mcp/server.ex"],"programRoutines":[{"name":"'Elixir.AshAi.Mcp.Server':check_origin/2"},{"name":"'Elixir.AshAi.Mcp.Server':origin_allowed?/3"}],"repo":"https://github.com/ash-project/ash_ai"}],"references":[{"url":"https://github.com/ash-project/ash_ai/security/advisories/GHSA-c92r-f3rr-q49h","tags":["vendor-advisory","related"]},{"url":"https://cna.erlef.org/cves/CVE-2026-81315.html","tags":["related"]},{"url":"https://osv.dev/vulnerability/EEF-CVE-2026-81315","tags":["related"]},{"url":"https://github.com/ash-project/ash_ai/commit/28af68d73134df0b8fb3aa6ab03e8fd795b07c21","tags":["patch"]}],"metrics":[{"cvssV4_0":{"Automatable":"NOT_DEFINED","Recovery":"NOT_DEFINED","Safety":"NOT_DEFINED","attackComplexity":"LOW","attackRequirements":"PRESENT","attackVector":"NETWORK","baseScore":7.4,"baseSeverity":"HIGH","privilegesRequired":"NONE","providerUrgency":"NOT_DEFINED","subAvailabilityImpact":"NONE","subConfidentialityImpact":"NONE","subIntegrityImpact":"NONE","userInteraction":"ACTIVE","valueDensity":"NOT_DEFINED","vectorString":"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","version":"4.0","vulnAvailabilityImpact":"NONE","vulnConfidentialityImpact":"HIGH","vulnIntegrityImpact":"HIGH","vulnerabilityResponseEffort":"NOT_DEFINED"},"format":"CVSS","scenarios":[{"lang":"en","value":"GENERAL"}]}],"problemTypes":[{"descriptions":[{"cweId":"CWE-346","description":"CWE-346 Origin Validation Error","lang":"en","type":"CWE"}]}],"providerMetadata":{"shortName":"EEF","orgId":"6b3ad84c-e1a6-4bf7-a703-f496b71e49db","dateUpdated":"2026-08-31T00:57:55.910Z"},"cpeApplicability":[{"nodes":[{"cpeMatch":[{"criteria":"cpe:2.3:a:ash-project:ash_ai:*:*:*:*:*:*:*:*","versionEndExcluding":"1.0.0","versionStartIncluding":"0.8.0","vulnerable":true}],"negate":false,"operator":"OR"}],"operator":"AND"}],"credits":[{"lang":"en","type":"finder","value":"Peter Ullrich"},{"lang":"en","type":"reporter","value":"Peter Ullrich"},{"lang":"en","type":"remediation developer","value":"Zach Daniel / Ash Project"},{"lang":"en","type":"coordinator","value":"Jonatan Männchen / EEF"}],"impacts":[{"capecId":"CAPEC-62","descriptions":[{"lang":"en","value":"CAPEC-62 Cross Site Request Forgery"}]}],"source":{"discovery":"EXTERNAL"}},"adp":[{"title":"CISA ADP Vulnrichment","references":[{"url":"https://github.com/ash-project/ash_ai/security/advisories/GHSA-c92r-f3rr-q49h","tags":["exploit"]}],"metrics":[{"other":{"type":"ssvc","content":{"timestamp":"2026-08-31T16:02:11.016935Z","id":"CVE-2026-81315","options":[{"Exploitation":"poc"},{"Automatable":"no"},{"Technical Impact":"total"}],"role":"CISA Coordinator","version":"2.0.3"}}}],"providerMetadata":{"shortName":"CISA-ADP","orgId":"134c704f-9b21-4f2e-91b3-4a467353bcc0","dateUpdated":"2026-08-31T16:02:38.700Z"}}]}}}