CVE-2026-81315 (GCVE-0-2026-81315)
Vulnerability from cvelistv5 – Published: 2026-08-31 00:57 – Updated: 2026-08-31 16:02
VLAI
EPSS
VEX
Title
MCP DNS-rebinding origin check in AshAi is bypassed by a spoofed X-Forwarded-Proto header
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.
Severity
SSVC
Exploitation: poc
Automatable: no
Technical Impact: total
CISA Coordinator · CISA-ADP (v2.0.3)
Decision recorded 2026-08-31 16:02 UTC
CWE
- CWE-346 - Origin Validation Error
Assigner
References
4 references
| URL | Tags |
|---|---|
| https://github.com/ash-project/ash_ai/security/ad… | vendor-advisoryrelated |
| 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/28af… | patch |
Impacted products
2 products
| Vendor | Product | Version | CPE status | |
|---|---|---|---|---|
| ash-project | ash_ai |
Affected:
0.8.0 , < 1.0.0
(semver)
cpe:2.3:a:ash-project:ash_ai:*:*:*:*:*:*:*:* |
||
| ash-project | ash_ai |
Affected:
c94f0b17fbe252f68755ba512678586164ba6139 , < 28af68d73134df0b8fb3aa6ab03e8fd795b07c21
(git)
cpe:2.3:a:ash-project:ash_ai:*:*:*:*:*:*:*:* |
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{
"lang": "en",
"type": "coordinator",
"value": "Jonatan M\u00e4nnchen / EEF"
}
],
"descriptions": [
{
"lang": "en",
"supportingMedia": [
{
"base64": false,
"type": "text/html",
"value": "\u003cp\u003eOrigin Validation Error vulnerability in ash-project ash_ai allows a malicious web page to bypass the MCP server\u0027s DNS-rebinding protection and issue cross-site requests to a user\u0027s local MCP server with that user\u0027s actor.\u003c/p\u003e\n\u003cp\u003eIn \u003ccode\u003eAshAi.Mcp.Server\u003c/code\u003e, with the default \u003ccode\u003eallowed_origins: nil\u003c/code\u003e, \u003ccode\u003eorigin_allowed?/3\u003c/code\u003e accepts an origin when \u003ccode\u003euri.host == conn.host\u003c/code\u003e and the forwarded scheme is \u003ccode\u003ehttps\u003c/code\u003e. Both values are attacker-controlled: \u003ccode\u003econn.host\u003c/code\u003e comes from the \u003ccode\u003eHost\u003c/code\u003e header and the scheme is read from the raw \u003ccode\u003ex-forwarded-proto\u003c/code\u003e header with no trusted-proxy check. Under DNS rebinding the browser sends the attacker\u0027s origin and a matching host, and page JavaScript may set \u003ccode\u003eX-Forwarded-Proto: https\u003c/code\u003e, so the check passes with no TLS or proxy involved. The fix trusts only localhost origins by default; other origins require an explicit \u003ccode\u003eallowed_origins\u003c/code\u003e allowlist.\u003c/p\u003e\n\u003cp\u003eThis issue affects ash_ai: from 0.8.0 before 1.0.0.\u003c/p\u003e"
},
{
"base64": false,
"type": "text/markdown",
"value": "Origin Validation Error vulnerability in ash-project ash_ai allows a malicious web page to bypass the MCP server\u0027s DNS-rebinding protection and issue cross-site requests to a user\u0027s local MCP server with that user\u0027s actor.\n\nIn `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\u0027s 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."
}
],
"value": "Origin Validation Error vulnerability in ash-project ash_ai allows a malicious web page to bypass the MCP server\u0027s DNS-rebinding protection and issue cross-site requests to a user\u0027s local MCP server with that user\u0027s actor.\n\nIn 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\u0027s 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."
}
],
"impacts": [
{
"capecId": "CAPEC-62",
"descriptions": [
{
"lang": "en",
"value": "CAPEC-62 Cross Site Request Forgery"
}
]
}
],
"metrics": [
{
"cvssV4_0": {
"Automatable": "NOT_DEFINED",
"Recovery": "NOT_DEFINED",
"Safety": "NOT_DEFINED",
"attackComplexity": "LOW",
"attackRequirements": "PRESENT",
"attackVector": "NETWORK",
"baseScore": 7.4,
"baseSeverity": "HIGH",
"privilegesRequired": "NONE",
"providerUrgency": "NOT_DEFINED",
"subAvailabilityImpact": "NONE",
"subConfidentialityImpact": "NONE",
"subIntegrityImpact": "NONE",
"userInteraction": "ACTIVE",
"valueDensity": "NOT_DEFINED",
"vectorString": "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",
"version": "4.0",
"vulnAvailabilityImpact": "NONE",
"vulnConfidentialityImpact": "HIGH",
"vulnIntegrityImpact": "HIGH",
"vulnerabilityResponseEffort": "NOT_DEFINED"
},
"format": "CVSS",
"scenarios": [
{
"lang": "en",
"value": "GENERAL"
}
]
}
],
"problemTypes": [
{
"descriptions": [
{
"cweId": "CWE-346",
"description": "CWE-346 Origin Validation Error",
"lang": "en",
"type": "CWE"
}
]
}
],
"providerMetadata": {
"dateUpdated": "2026-08-31T00:57:55.910Z",
"orgId": "6b3ad84c-e1a6-4bf7-a703-f496b71e49db",
"shortName": "EEF"
},
"references": [
{
"tags": [
"vendor-advisory",
"related"
],
"url": "https://github.com/ash-project/ash_ai/security/advisories/GHSA-c92r-f3rr-q49h"
},
{
"tags": [
"related"
],
"url": "https://cna.erlef.org/cves/CVE-2026-81315.html"
},
{
"tags": [
"related"
],
"url": "https://osv.dev/vulnerability/EEF-CVE-2026-81315"
},
{
"tags": [
"patch"
],
"url": "https://github.com/ash-project/ash_ai/commit/28af68d73134df0b8fb3aa6ab03e8fd795b07c21"
}
],
"source": {
"discovery": "EXTERNAL"
},
"title": "MCP DNS-rebinding origin check in AshAi is bypassed by a spoofed X-Forwarded-Proto header"
}
},
"cveMetadata": {
"assignerOrgId": "6b3ad84c-e1a6-4bf7-a703-f496b71e49db",
"assignerShortName": "EEF",
"cveId": "CVE-2026-81315",
"datePublished": "2026-08-31T00:57:55.910Z",
"dateReserved": "2026-08-30T20:00:01.860Z",
"dateUpdated": "2026-08-31T16:02:38.700Z",
"state": "PUBLISHED"
},
"dataType": "CVE_RECORD",
"dataVersion": "5.2"
}
}
}
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Drag nodes to arrange them. Double-click a related vulnerability to open it, or a source to visit its link. The Physics button on the left tunes the layout and the simulation; the legend at the bottom left hides or shows nodes by kind and by sighting type.
Experimental. This forecast is provided for visualization only and may change without notice. Do not use it for operational decisions.
Forecast uses a logistic model when the trend is rising, or an exponential decay model when the trend is falling. Fitted via linearized least squares.
Sightings
| Author | Source | Type | Date | Other |
|---|
Nomenclature
- Seen: The vulnerability was mentioned, discussed, or observed by the user.
- Confirmed: The vulnerability has been validated from an analyst's perspective.
- Published Proof of Concept: A public proof of concept is available for this vulnerability.
- Exploited: The vulnerability was observed as exploited by the user who reported the sighting.
- Patched: The vulnerability was observed as successfully patched by the user who reported the sighting.
- Not exploited: The vulnerability was not observed as exploited by the user who reported the sighting.
- Not confirmed: The user expressed doubt about the validity of the vulnerability.
- Not patched: The vulnerability was not observed as successfully patched by the user who reported the sighting.
Vulnerability timeline
Sightings and recorded dates, grouped by day · UTC
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The MITRE ATT&CK techniques below are AI-generated suggestions, inferred from the description of the
vulnerability by the CIRCL/vulnerability-attack-technique-classification-roberta-base
model, served locally by ML-Gateway.
They have not been verified by an analyst and are provided for guidance only.
The approach is described in our paper Mapping CVEs to MITRE ATT&CK Techniques: A Curated Gold-Set Classifier and the Limits of LLM-Assisted Label Expansion.
Browse all ATT&CK techniques and the vulnerabilities related to each.
The approach is described in our paper Mapping CVEs to MITRE ATT&CK Techniques: A Curated Gold-Set Classifier and the Limits of LLM-Assisted Label Expansion.
Browse all ATT&CK techniques and the vulnerabilities related to each.
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Related by attack behaviour
Vulnerabilities whose description is nearest to this one in the vector space of the CIRCL/vulnerability-attack-technique-biencoder model. This is a similarity search over the bi-encoder space (plain cosine), not a classification, and it has no measured accuracy.