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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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      "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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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.


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.