CVE-2026-81315 (GCVE-0-2026-81315)

Vulnerability from cvelistv5 – Published: 2026-08-31 00:57 – Updated: 2026-08-31 16:02
VLAI
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
7.4 (High)
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
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
Impacted 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:*:*:*:*:*:*:*:*
Create a notification for this product.
ash-project ash_ai Affected: c94f0b17fbe252f68755ba512678586164ba6139 , < 28af68d73134df0b8fb3aa6ab03e8fd795b07c21 (git)
    cpe:2.3:a:ash-project:ash_ai:*:*:*:*:*:*:*:*
Create a notification for this product.
Credits
Peter Ullrich Peter Ullrich Zach Daniel / Ash Project Jonatan Männchen / EEF
Show details on NVD website
To clipboard 

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      "containers": "{\"adp\": [{\"title\": \"CISA ADP Vulnrichment\", \"metrics\": [{\"other\": {\"type\": \"ssvc\", \"content\": {\"id\": \"CVE-2026-81315\", \"role\": \"CISA Coordinator\", \"options\": [{\"Exploitation\": \"poc\"}, {\"Automatable\": \"no\"}, {\"Technical Impact\": \"total\"}], \"version\": \"2.0.3\", \"timestamp\": \"2026-08-31T16:02:11.016935Z\"}}}], \"references\": [{\"url\": \"https://github.com/ash-project/ash_ai/security/advisories/GHSA-c92r-f3rr-q49h\", \"tags\": [\"exploit\"]}], \"providerMetadata\": {\"orgId\": \"134c704f-9b21-4f2e-91b3-4a467353bcc0\", \"shortName\": \"CISA-ADP\", \"dateUpdated\": \"2026-08-31T16:02:32.413Z\"}}], \"cna\": {\"title\": \"MCP DNS-rebinding origin check in AshAi is bypassed by a spoofed X-Forwarded-Proto header\", \"source\": {\"discovery\": \"EXTERNAL\"}, \"credits\": [{\"lang\": \"en\", \"type\": \"finder\", \"value\": \"Peter Ullrich\"}, {\"lang\": \"en\", \"type\": \"reporter\", \"value\": \"Peter Ullrich\"}, {\"lang\": \"en\", \"type\": \"remediation developer\", \"value\": \"Zach Daniel / Ash Project\"}, {\"lang\": \"en\", \"type\": \"coordinator\", \"value\": \"Jonatan M\\u00e4nnchen / EEF\"}], \"impacts\": [{\"capecId\": \"CAPEC-62\", \"descriptions\": [{\"lang\": \"en\", \"value\": \"CAPEC-62 Cross Site Request Forgery\"}]}], \"metrics\": [{\"format\": \"CVSS\", \"cvssV4_0\": {\"Safety\": \"NOT_DEFINED\", \"version\": \"4.0\", \"Recovery\": \"NOT_DEFINED\", \"baseScore\": 7.4, \"Automatable\": \"NOT_DEFINED\", \"attackVector\": \"NETWORK\", \"baseSeverity\": \"HIGH\", \"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\", \"providerUrgency\": \"NOT_DEFINED\", \"userInteraction\": \"ACTIVE\", \"attackComplexity\": \"LOW\", \"attackRequirements\": \"PRESENT\", \"privilegesRequired\": \"NONE\", \"subIntegrityImpact\": \"NONE\", \"vulnIntegrityImpact\": \"HIGH\", \"subAvailabilityImpact\": \"NONE\", \"vulnAvailabilityImpact\": \"NONE\", \"subConfidentialityImpact\": \"NONE\", \"vulnConfidentialityImpact\": \"HIGH\", \"vulnerabilityResponseEffort\": \"NOT_DEFINED\"}, \"scenarios\": [{\"lang\": \"en\", \"value\": \"GENERAL\"}]}], \"affected\": [{\"cpes\": [\"cpe:2.3:a:ash-project:ash_ai:*:*:*:*:*:*:*:*\"], \"repo\": \"https://github.com/ash-project/ash_ai\", \"vendor\": \"ash-project\", \"modules\": [\"\u0027Elixir.AshAi.Mcp.Server\u0027\"], \"product\": \"ash_ai\", \"versions\": [{\"status\": \"affected\", \"version\": \"0.8.0\", \"lessThan\": \"1.0.0\", \"versionType\": \"semver\"}], \"packageURL\": \"pkg:hex/ash_ai\", \"packageName\": \"ash_ai\", \"programFiles\": [\"lib/ash_ai/mcp/server.ex\"], \"collectionURL\": \"https://repo.hex.pm\", \"defaultStatus\": \"unaffected\", \"programRoutines\": [{\"name\": \"\u0027Elixir.AshAi.Mcp.Server\u0027:check_origin/2\"}, {\"name\": \"\u0027Elixir.AshAi.Mcp.Server\u0027:origin_allowed?/3\"}]}, {\"cpes\": [\"cpe:2.3:a:ash-project:ash_ai:*:*:*:*:*:*:*:*\"], \"repo\": \"https://github.com/ash-project/ash_ai\", \"vendor\": \"ash-project\", \"modules\": [\"\u0027Elixir.AshAi.Mcp.Server\u0027\"], \"product\": \"ash_ai\", \"versions\": [{\"status\": \"affected\", \"version\": \"c94f0b17fbe252f68755ba512678586164ba6139\", \"lessThan\": \"28af68d73134df0b8fb3aa6ab03e8fd795b07c21\", \"versionType\": \"git\"}], \"packageURL\": \"pkg:github/ash-project/ash_ai\", \"packageName\": \"ash-project/ash_ai\", \"programFiles\": [\"lib/ash_ai/mcp/server.ex\"], \"collectionURL\": \"https://github.com\", \"defaultStatus\": \"unaffected\", \"programRoutines\": [{\"name\": \"\u0027Elixir.AshAi.Mcp.Server\u0027:check_origin/2\"}, {\"name\": \"\u0027Elixir.AshAi.Mcp.Server\u0027:origin_allowed?/3\"}]}], \"references\": [{\"url\": \"https://github.com/ash-project/ash_ai/security/advisories/GHSA-c92r-f3rr-q49h\", \"tags\": [\"vendor-advisory\", \"related\"]}, {\"url\": \"https://cna.erlef.org/cves/CVE-2026-81315.html\", \"tags\": [\"related\"]}, {\"url\": \"https://osv.dev/vulnerability/EEF-CVE-2026-81315\", \"tags\": [\"related\"]}, {\"url\": \"https://github.com/ash-project/ash_ai/commit/28af68d73134df0b8fb3aa6ab03e8fd795b07c21\", \"tags\": [\"patch\"]}], \"descriptions\": [{\"lang\": \"en\", \"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. 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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. 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      "cveMetadata": "{\"cveId\": \"CVE-2026-81315\", \"state\": \"PUBLISHED\", \"dateUpdated\": \"2026-08-31T16:02:38.700Z\", \"dateReserved\": \"2026-08-30T20:00:01.860Z\", \"assignerOrgId\": \"6b3ad84c-e1a6-4bf7-a703-f496b71e49db\", \"datePublished\": \"2026-08-31T00:57:55.910Z\", \"assignerShortName\": \"EEF\"}",
      "dataType": "CVE_RECORD",
      "dataVersion": "5.2"
    }
  }
}



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Taxonomy of the tags.





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.


Detection rules are retrieved from Rulezet.