CVE-2026-81315

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.

CVSS

No CVSS.

References

Link	Resource
https://cna.erlef.org/cves/CVE-2026-81315.html
https://github.com/ash-project/ash_ai/commit/28af68d73134df0b8fb3aa6ab03e8fd795b07c21
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

Configurations

No configuration.

History

No history.

Information

Published : 2026-08-31 01:16

Updated : 2026-09-01 21:15

NVD link : CVE-2026-81315

Mitre link : CVE-2026-81315

CVE.ORG link : CVE-2026-81315

JSON object : View

Products Affected

No product.

CWE

CWE-346

Origin Validation Error

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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."}], "lastModified": "2026-09-01T21:15:00.147", "sourceIdentifier": "6b3ad84c-e1a6-4bf7-a703-f496b71e49db"}