CVE-2026-8466

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Deployments that do not handle multipart uploads are not affected.</p>"}], "value": "The application must expose an HTTP endpoint that calls cowboy_req:read_part/1,2 to process multipart/form-data request bodies. Deployments that do not handle multipart uploads are not affected."}], "cpeApplicability": [{"nodes": [{"cpeMatch": [{"criteria": "cpe:2.3:a:ninenines:cowboy:*:*:*:*:*:*:*:*", "versionEndExcluding": "2.15.0", "versionStartIncluding": "2.0.0", "vulnerable": true}], "negate": false, "operator": "OR"}]}], "credits": [{"lang": "en", "type": "finder", "value": "Peter Ullrich"}, {"lang": "en", "type": "remediation developer", "value": "Lo\u00efc Hoguin"}], "descriptions": [{"lang": "en", "supportingMedia": [{"base64": false, "type": "text/html", "value": "<p>Allocation of Resources Without Limits or Throttling vulnerability in ninenines cowboy allows denial of service via unbounded buffer accumulation in multipart header parsing.</p><p><tt>cowboy_req:read_part/3</tt> in <tt>src/cowboy_req.erl</tt> accumulates incoming request bytes into a <tt>Buffer</tt> binary with no upper-bound check. When <tt>cow_multipart:parse_headers/2</tt> returns <tt>more</tt> or <tt>{more, Buffer2}</tt>, the function reads up to <tt>Length</tt> bytes (default 64 KB) from the request body and recurses with the enlarged buffer. There is no equivalent of the <tt>byte_size(Acc) &gt; Length</tt> guard present in the sibling function <tt>read_part_body/4</tt>. An unauthenticated attacker can send a <tt>multipart/form-data</tt> request whose body never yields a complete header section \u2014 for example, a body that never contains the advertised boundary delimiter, or one whose header lines never contain <tt>\\r\\n\\r\\n</tt> \u2014 and force the server process to accumulate memory linearly with the bytes the protocol layer is willing to deliver. A handful of concurrent such uploads is sufficient to exhaust BEAM memory.</p><p>This issue affects cowboy from 2.0.0 before 2.15.0.</p>"}], "value": "Allocation of Resources Without Limits or Throttling vulnerability in ninenines cowboy allows denial of service via unbounded buffer accumulation in multipart header parsing.\n\ncowboy_req:read_part/3 in src/cowboy_req.erl accumulates incoming request bytes into a Buffer binary with no upper-bound check. When cow_multipart:parse_headers/2 returns more or {more, Buffer2}, the function reads up to Length bytes (default 64 KB) from the request body and recurses with the enlarged buffer. There is no equivalent of the byte_size(Acc) > Length guard present in the sibling function read_part_body/4. An unauthenticated attacker can send a multipart/form-data request whose body never yields a complete header section \u2014 for example, a body that never contains the advertised boundary delimiter, or one whose header lines never contain \\r\\n\\r\\n \u2014 and force the server process to accumulate memory linearly with the bytes the protocol layer is willing to deliver. A handful of concurrent such uploads is sufficient to exhaust BEAM memory.\n\nThis issue affects cowboy from 2.0.0 before 2.15.0."}], "impacts": [{"capecId": "CAPEC-130", "descriptions": [{"lang": "en", "value": "CAPEC-130 Excessive Allocation"}]}], "metrics": [{"cvssV4_0": {"attackComplexity": "LOW", "attackRequirements": "PRESENT", "attackVector": "NETWORK", "baseScore": 8.2, "baseSeverity": "HIGH", "privilegesRequired": "NONE", "subAvailabilityImpact": "NONE", "subConfidentialityImpact": "NONE", "subIntegrityImpact": "NONE", "userInteraction": "NONE", "vectorString": "CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N", "version": "4.0", "vulnAvailabilityImpact": "HIGH", "vulnConfidentialityImpact": "NONE", "vulnIntegrityImpact": "NONE"}, "format": "CVSS", "scenarios": [{"lang": "en", "value": "GENERAL"}]}], "problemTypes": [{"descriptions": [{"cweId": "CWE-770", "description": "CWE-770 Allocation of Resources Without Limits or Throttling", "lang": "en", "type": "CWE"}]}], "providerMetadata": {"orgId": "6b3ad84c-e1a6-4bf7-a703-f496b71e49db", "shortName": "EEF", "dateUpdated": "2026-05-14T04:30:32.552Z"}, "references": [{"tags": ["related", "third-party-advisory"], "url": "https://cna.erlef.org/cves/CVE-2026-8466.html"}, {"tags": ["related"], "url": "https://osv.dev/vulnerability/EEF-CVE-2026-8466"}, {"tags": ["patch"], "url": "https://github.com/ninenines/cowboy/commit/5c6a2061b41bb5771c4659fac7d5a822dca5bafb"}], "source": {"discovery": "EXTERNAL"}, "title": "Unbounded buffer accumulation in multipart header parsing causes denial of service in cowboy", "x_generator": {"engine": "cvelib 1.8.0"}}, "adp": [{"metrics": [{"other": {"type": "ssvc", "content": {"timestamp": "2026-05-13T18:46:37.406887Z", "id": "CVE-2026-8466", "options": [{"Exploitation": "none"}, {"Automatable": "no"}, {"Technical Impact": "partial"}], "role": "CISA Coordinator", "version": "2.0.3"}}}], "title": "CISA ADP Vulnrichment", "providerMetadata": {"orgId": "134c704f-9b21-4f2e-91b3-4a467353bcc0", "shortName": "CISA-ADP", "dateUpdated": "2026-05-13T18:52:29.452Z"}}]}}

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When cow_multipart:parse_headers/2 returns more or {more, Buffer2}, the function reads up to Length bytes (default 64 KB) from the request body and recurses with the enlarged buffer. There is no equivalent of the byte_size(Acc) > Length guard present in the sibling function read_part_body/4. An unauthenticated attacker can send a multipart/form-data request whose body never yields a complete header section \u2014 for example, a body that never contains the advertised boundary delimiter, or one whose header lines never contain \\r\\n\\r\\n \u2014 and force the server process to accumulate memory linearly with the bytes the protocol layer is willing to deliver. A handful of concurrent such uploads is sufficient to exhaust BEAM memory.\n\nThis issue affects cowboy from 2.0.0 before 2.15.0.", "supportingMedia": [{"type": "text/html", "value": "<p>Allocation of Resources Without Limits or Throttling vulnerability in ninenines cowboy allows denial of service via unbounded buffer accumulation in multipart header parsing.</p><p><tt>cowboy_req:read_part/3</tt> in <tt>src/cowboy_req.erl</tt> accumulates incoming request bytes into a <tt>Buffer</tt> binary with no upper-bound check. When <tt>cow_multipart:parse_headers/2</tt> returns <tt>more</tt> or <tt>{more, Buffer2}</tt>, the function reads up to <tt>Length</tt> bytes (default 64 KB) from the request body and recurses with the enlarged buffer. There is no equivalent of the <tt>byte_size(Acc) &gt; Length</tt> guard present in the sibling function <tt>read_part_body/4</tt>. An unauthenticated attacker can send a <tt>multipart/form-data</tt> request whose body never yields a complete header section \u2014 for example, a body that never contains the advertised boundary delimiter, or one whose header lines never contain <tt>\\r\\n\\r\\n</tt> \u2014 and force the server process to accumulate memory linearly with the bytes the protocol layer is willing to deliver. A handful of concurrent such uploads is sufficient to exhaust BEAM memory.</p><p>This issue affects cowboy from 2.0.0 before 2.15.0.</p>", "base64": false}]}], "problemTypes": [{"descriptions": [{"lang": "en", "type": "CWE", "cweId": "CWE-770", "description": "CWE-770 Allocation of Resources Without Limits or Throttling"}]}], "configurations": [{"lang": "en", "value": "The application must expose an HTTP endpoint that calls cowboy_req:read_part/1,2 to process multipart/form-data request bodies. 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When cow_multipart:parse_headers/2 returns more or {more, Buffer2}, the function reads up to Length bytes (default 64 KB) from the request body and recurses with the enlarged buffer. There is no equivalent of the byte_size(Acc) > Length guard present in the sibling function read_part_body/4. An unauthenticated attacker can send a multipart/form-data request whose body never yields a complete header section \u2014 for example, a body that never contains the advertised boundary delimiter, or one whose header lines never contain \\r\\n\\r\\n \u2014 and force the server process to accumulate memory linearly with the bytes the protocol layer is willing to deliver. A handful of concurrent such uploads is sufficient to exhaust BEAM memory.\n\nThis issue affects cowboy from 2.0.0 before 2.15.0."}, {"lang": "es", "value": "La vulnerabilidad de asignaci\u00f3n de recursos sin l\u00edmites ni limitaci\u00f3n en ninenines cowboy permite la denegaci\u00f3n de servicio a trav\u00e9s de la acumulaci\u00f3n ilimitada de b\u00fafer en el an\u00e1lisis de encabezados multipart.\n\ncowboy_req:read_part/3 en src/cowboy_req.erl acumula bytes de solicitud entrantes en un binario de b\u00fafer sin una comprobaci\u00f3n de l\u00edmite superior. Cuando cow_multipart:parse_headers/2 devuelve more o {more, Buffer2}, la funci\u00f3n lee hasta Length bytes (64 KB por defecto) del cuerpo de la solicitud y recurre con el b\u00fafer ampliado. No existe un equivalente de la guarda byte_size(Acc) > Length presente en la funci\u00f3n hermana read_part_body/4. Un atacante no autenticado puede enviar una solicitud multipart/form-data cuyo cuerpo nunca produce una secci\u00f3n de encabezado completa - por ejemplo, un cuerpo que nunca contiene el delimitador de l\u00edmite anunciado, o uno cuyas l\u00edneas de encabezado nunca contienen \\r\\n\\r\\n - y forzar al proceso del servidor a acumular memoria linealmente con los bytes que la capa del protocolo est\u00e1 dispuesta a entregar. Un pu\u00f1ado de dichas cargas concurrentes es suficiente para agotar la memoria BEAM.\n\nEste problema afecta a cowboy desde 2.0.0 antes de 2.15.0."}], "id": "CVE-2026-8466", "lastModified": "2026-10-26T14:10:00.130", "metrics": {"cvssMetricV40": [{"cvssData": {"Automatable": "NOT_DEFINED", "Recovery": "NOT_DEFINED", "Safety": "NOT_DEFINED", "attackComplexity": "LOW", "attackRequirements": "PRESENT", "attackVector": "NETWORK", "availabilityRequirement": "NOT_DEFINED", "baseScore": 8.2, "baseSeverity": "HIGH", "confidentialityRequirement": "NOT_DEFINED", "exploitMaturity": "NOT_DEFINED", "integrityRequirement": "NOT_DEFINED", "modifiedAttackComplexity": "NOT_DEFINED", "modifiedAttackRequirements": "NOT_DEFINED", "modifiedAttackVector": "NOT_DEFINED", "modifiedPrivilegesRequired": "NOT_DEFINED", "modifiedSubAvailabilityImpact": "NOT_DEFINED", "modifiedSubConfidentialityImpact": "NOT_DEFINED", "modifiedSubIntegrityImpact": "NOT_DEFINED", "modifiedUserInteraction": "NOT_DEFINED", "modifiedVulnAvailabilityImpact": "NOT_DEFINED", "modifiedVulnConfidentialityImpact": "NOT_DEFINED", "modifiedVulnIntegrityImpact": "NOT_DEFINED", "privilegesRequired": "NONE", "providerUrgency": "NOT_DEFINED", "subAvailabilityImpact": "NONE", "subConfidentialityImpact": "NONE", "subIntegrityImpact": "NONE", "userInteraction": "NONE", "valueDensity": "NOT_DEFINED", "vectorString": "CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X", "version": "4.0", "vulnAvailabilityImpact": "HIGH", "vulnConfidentialityImpact": "NONE", "vulnIntegrityImpact": "NONE", "vulnerabilityResponseEffort": "NOT_DEFINED"}, "source": "6b3ad84c-e1a6-4bf7-a703-f496b71e49db", "type": "Secondary"}], "ssvcV203": [{"source": "134c704f-9b21-4f2e-91b3-4a467353bcc0", "ssvcData": {"id": "CVE-2026-8466", "options": [{"exploitation": "none"}, {"automatable": "no"}, {"technicalImpact": "partial"}], "role": "CISA Coordinator", "timestamp": "2026-05-13T18:46:37.406887Z", "version": "2.0.3"}}]}, "published": "2026-05-13T19:17:30.540", "references": [{"source": "6b3ad84c-e1a6-4bf7-a703-f496b71e49db", "url": "https://cna.erlef.org/cves/CVE-2026-8466.html"}, {"source": "6b3ad84c-e1a6-4bf7-a703-f496b71e49db", "url": "https://github.com/ninenines/cowboy/commit/5c6a2061b41bb5771c4659fac7d5a822dca5bafb"}, {"source": "6b3ad84c-e1a6-4bf7-a703-f496b71e49db", "url": "https://osv.dev/vulnerability/EEF-CVE-2026-8466"}], "sourceIdentifier": "6b3ad84c-e1a6-4bf7-a703-f496b71e49db", "vulnStatus": "Deferred", "weaknesses": [{"description": [{"lang": "en", "value": "CWE-770"}], "source": "6b3ad84c-e1a6-4bf7-a703-f496b71e49db", "type": "Secondary"}]}

{}

{"affected": [{"configurations": [{"platform": null, "status": "affected", "versions": {"scheme": "semver", "value": "[2.0.0,2.15.0)"}}, {"platform": null, "status": "affected", "versions": {"scheme": "code_commit", "value": "[917cf99e10c41676183d501b86af6e47c95afb89,5c6a2061b41bb5771c4659fac7d5a822dca5bafb)"}}], "enrichment": {"confidence": 95.0, "confidence_source": "inferred", "scores": [{"score": 95.0, "source": "inferred"}]}, "product": "cowboy", "vendor": "ninenines"}], "created": "2026-05-13T20:00:04.255907+00:00", "updated": "2026-05-14T14:33:56.676405+00:00", "vendors": ["ninenines", "ninenines$PRODUCT$cowboy"]}