EEF-CVE-2026-81315
MCP DNS-rebinding origin check in AshAi is bypassed by a spoofed X-Forwarded-Proto header
Quick fix
EEF-CVE-2026-81315 — ash_ai: upgrade to the fixed version with the command below.
mix deps.update ash_aiDetails
## Summary
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.
In 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.
This issue affects ash\_ai: from 0.8.0 before 1.0.0.
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