Vulnerability 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. 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.
Related Weaknesses (CWE)
References
- https://cna.erlef.org/cves/CVE-2026-81315.html
- https://github.com/ash-project/ash_ai/commit/28af68d73134df0b8fb3aa6ab03e8fd795b
- https://github.com/ash-project/ash_ai/security/advisories/GHSA-c92r-f3rr-q49h
- https://osv.dev/vulnerability/EEF-CVE-2026-81315
- https://github.com/ash-project/ash_ai/security/advisories/GHSA-c92r-f3rr-q49h
FAQ
What is CVE-2026-81315?
CVE-2026-81315 is a documented vulnerability. 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 w...
How severe is CVE-2026-81315?
CVSS scoring is not yet available for CVE-2026-81315. Check NVD for updates.
Is there a patch for CVE-2026-81315?
Check the references section above for vendor advisories and patch information. Review vendor security bulletins for remediation guidance.