# CVE-2026-81315

## Summary

- **CVE ID:** CVE-2026-81315
- **Severity:** HIGH
- **CVSS Score:** 7.4 (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)
- **CWE:** CWE-346
- **Published:** Aug 31, 2026
- **Last Modified:** Aug 31, 2026

## 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

- ash-project — ash_ai (0.8.0)
- ash-project — ash_ai (c94f0b17fbe252f68755ba512678586164ba6139)

## References

- [CNA](https://github.com/ash-project/ash_ai/security/advisories/GHSA-c92r-f3rr-q49h)
- [CNA](https://cna.erlef.org/cves/CVE-2026-81315.html)
- [CNA](https://osv.dev/vulnerability/EEF-CVE-2026-81315)
- [CNA](https://github.com/ash-project/ash_ai/commit/28af68d73134df0b8fb3aa6ab03e8fd795b07c21)

## Exploitation Prediction (EPSS)

- **EPSS Score:** 0.19%
- **EPSS Percentile:** 8.8

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_Exported from OnDuty AI Vulnerability Intelligence on 2026-09-10._