CVE-2026-81315
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
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.
Affected Software
| Vendor | Product | Version Range | Status |
|---|---|---|---|
| ash-project | ash_ai | 0.8.0 < 1.0.0 | affected |
| ash-project | ash_ai | c94f0b17fbe252f68755ba512678586164ba6139 < 28af68d73134df0b8fb3aa6ab03e8fd795b07c21 | affected |
Weaknesses
- CWE-346: CWE-346 Origin Validation Error
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
Feedback
Was this page helpful?
Glad to hear it! Please tell us how we can improve.
Sorry to hear that. Please tell us how we can improve.