Vulnerability · Published Aug 31, 2026 · Assigned by EEF
CVE-2026-81315MCP DNS-rebinding origin check in AshAi is bypassed by a spoofed X-Forwarded-Proto header
High 7.4
In plain English
A high-severity security flaw in ash_ai from ash-project. Proof-of-concept exploit code is public. The chance it is exploited in the next 30 days is estimated at 0.3% (higher than 20% of all known vulnerabilities).
Official 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.
Affected products (as reported)
| Vendor | Product | Versions |
|---|---|---|
| ash-project | ash_ai | 0.8.0 – before 1.0.0 |
| ash-project | ash_ai | c94f0b17fbe252f68755ba512678586164ba6139 – before 28af68d73134df0b8fb3aa6ab03e8fd795b07c21 |
Weakness: CWE-346 · 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
References
- https://github.com/ash-project/ash_ai/security/advisories/GHSA-c92r-f3rr-q49h vendor-advisory, related
- https://cna.erlef.org/cves/CVE-2026-81315.html related
- https://osv.dev/vulnerability/EEF-CVE-2026-81315 related
- https://github.com/ash-project/ash_ai/commit/28af68d73134df0b8fb3aa6ab03e8fd795b07c21 patch