MCP DNS-rebinding origin check in AshAi is bypassed by a spoofed X-Forwarded-Proto header (CVE-2026-81315) | HOL Guard CVE

Unknown severity · Source severity not reportedCVE-2026-81315

MCP DNS-rebinding origin check in AshAi is bypassed by a spoofed X-Forwarded-Proto header

Answer in brief

CVE-2026-81315 records a Unknown severity vulnerability in MCP DNS-rebinding origin check in AshAi is bypassed by a spoofed X-Forwarded-Proto header. The current sources do not mark it as known exploited. The current feed maps ash-project/ash_ai (generic), ash-project/ash_ai (generic). Check affected ranges and fixed versions before updating.

Analysis pending evidence review

HOL Guard separates source facts from reviewed analysis. See the methodology.

Published Aug 31, 2026Updated Aug 31, 2026Source checked Aug 31, 2026First seen by HOL Aug 31, 2026Material review Aug 31, 2026

Upstream Advisory

Key facts

Risk: Unknown severitySource severity not reported
Exploitation: Not marked as known exploited
Affected software: 2 mapped packages or products
Fix availability: Available

Why this deserves its current priority

A CVSS score is not reported in the current record. The current sources do not mark it as known exploited. Treat this as a source-backed prioritization signal, not a statement about your environment.

Analysis status

Analysis pending evidence review

Factual feed record only; HOL analysis is not approved for indexing. Read the methodology.

Affected scope and exposure questions

The current feed maps ash-project/ash_ai (generic), ash-project/ash_ai (generic). Check affected ranges and fixed versions before updating.

Mapped affected packages and fixed versions
Package	Affected range	Fixed version
ash-project/ash_aigeneric	>=0.8.0 <1.0.0	1.0.0
ash-project/ash_aigeneric	>=c94f0b17fbe252f68755ba512678586164ba6139 <28af68d73134df0b8fb3aa6ab03e8fd795b07c21	28af68d73134df0b8fb3aa6ab03e8fd795b07c21

Recommended response

Check inventory. Check lockfiles and deployed manifests for ash-project/ash_ai, ash-project/ash_ai.
Review the reported fix. Update ash-project/ash_ai to 1.0.0; ash-project/ash_ai to 28af68d73134df0b8fb3aa6ab03e8fd795b07c21 if you use the affected versions. Test the change in a non-production environment first.

Evidence timeline and material changes

Published upstream
Aug 31, 2026
Evidence: source:cvelist:source_dates:source-dates:record
Source modified
Aug 31, 2026
Evidence: source:cvelist:source_dates:source-dates:record
First seen by HOL
Aug 31, 2026

Sources and claim methodology

Upstream source 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.

Quoted source text, attributed separately from HOL analysis.