{"id":"CVE-2026-8466","state":"PUBLISHED","title":"Unbounded buffer accumulation in multipart header parsing causes denial of service in cowboy","description":"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 — for example, a body that never contains the advertised boundary delimiter, or one whose header lines never contain \\r\\n\\r\\n — 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.","publishedAt":"2026-05-13T18:26:21.089Z","updatedAt":"2026-05-14T04:30:32.552Z","severity":{"score":8.2,"label":"High","version":"4.0","vector":"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","source":"EEF"},"assigner":"EEF","products":["ninenines cowboy"],"affected":[{"vendor":"ninenines","product":"cowboy","packageName":"cowboy","packageURL":"pkg:hex/cowboy","defaultStatus":"unaffected","versions":[{"version":"2.0.0","status":"affected","lessThan":"2.15.0","versionType":"semver"}],"collectionURL":"https://repo.hex.pm","cpes":["cpe:2.3:a:ninenines:cowboy:*:*:*:*:*:*:*:*"],"modules":["cowboy_req"],"programFiles":["src/cowboy_req.erl"],"programRoutines":[{"name":"cowboy_req:read_part/1"},{"name":"cowboy_req:read_part/2"},{"name":"cowboy_req:read_part/3"}],"repo":"https://github.com/ninenines/cowboy"},{"vendor":"ninenines","product":"cowboy","packageName":"ninenines/cowboy","packageURL":"pkg:github/ninenines/cowboy","defaultStatus":"unaffected","versions":[{"version":"917cf99e10c41676183d501b86af6e47c95afb89","status":"affected","lessThan":"5c6a2061b41bb5771c4659fac7d5a822dca5bafb","versionType":"git"}],"collectionURL":"https://github.com","cpes":["cpe:2.3:a:ninenines:cowboy:*:*:*:*:*:*:*:*"],"modules":["cowboy_req"],"programFiles":["src/cowboy_req.erl"],"programRoutines":[{"name":"cowboy_req:read_part/1"},{"name":"cowboy_req:read_part/2"},{"name":"cowboy_req:read_part/3"}],"repo":"https://github.com/ninenines/cowboy"}],"references":["https://cna.erlef.org/cves/CVE-2026-8466.html","https://osv.dev/vulnerability/EEF-CVE-2026-8466","https://github.com/ninenines/cowboy/commit/5c6a2061b41bb5771c4659fac7d5a822dca5bafb"],"weaknesses":["CWE-770"],"ingestedAt":"2026-10-29T20:13:26.108Z","source":{"repository":"CVEProject/cvelistV5","path":"cves/2026/8xxx/CVE-2026-8466.json","commit":"556c9d3a8cd17e218bb8e452ba7cd619a384ff47"},"raw":{"dataType":"CVE_RECORD","dataVersion":"5.2","cveMetadata":{"cveId":"CVE-2026-8466","state":"PUBLISHED","datePublished":"2026-05-13T18:26:21.089Z","dateUpdated":"2026-05-14T04:30:32.552Z","assignerShortName":"EEF","assignerOrgId":"6b3ad84c-e1a6-4bf7-a703-f496b71e49db","dateReserved":"2026-05-13T11:44:39.149Z"},"containers":{"cna":{"title":"Unbounded buffer accumulation in multipart header parsing causes denial of service in cowboy","descriptions":[{"lang":"en","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 — for example, a body that never contains the advertised boundary delimiter, or one whose header lines never contain \\r\\n\\r\\n — 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."}],"affected":[{"vendor":"ninenines","product":"cowboy","packageName":"cowboy","packageURL":"pkg:hex/cowboy","defaultStatus":"unaffected","versions":[{"version":"2.0.0","status":"affected","lessThan":"2.15.0","versionType":"semver"}],"collectionURL":"https://repo.hex.pm","cpes":["cpe:2.3:a:ninenines:cowboy:*:*:*:*:*:*:*:*"],"modules":["cowboy_req"],"programFiles":["src/cowboy_req.erl"],"programRoutines":[{"name":"cowboy_req:read_part/1"},{"name":"cowboy_req:read_part/2"},{"name":"cowboy_req:read_part/3"}],"repo":"https://github.com/ninenines/cowboy"},{"vendor":"ninenines","product":"cowboy","packageName":"ninenines/cowboy","packageURL":"pkg:github/ninenines/cowboy","defaultStatus":"unaffected","versions":[{"version":"917cf99e10c41676183d501b86af6e47c95afb89","status":"affected","lessThan":"5c6a2061b41bb5771c4659fac7d5a822dca5bafb","versionType":"git"}],"collectionURL":"https://github.com","cpes":["cpe:2.3:a:ninenines:cowboy:*:*:*:*:*:*:*:*"],"modules":["cowboy_req"],"programFiles":["src/cowboy_req.erl"],"programRoutines":[{"name":"cowboy_req:read_part/1"},{"name":"cowboy_req:read_part/2"},{"name":"cowboy_req:read_part/3"}],"repo":"https://github.com/ninenines/cowboy"}],"references":[{"url":"https://cna.erlef.org/cves/CVE-2026-8466.html","tags":["related","third-party-advisory"]},{"url":"https://osv.dev/vulnerability/EEF-CVE-2026-8466","tags":["related"]},{"url":"https://github.com/ninenines/cowboy/commit/5c6a2061b41bb5771c4659fac7d5a822dca5bafb","tags":["patch"]}],"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":{"shortName":"EEF","orgId":"6b3ad84c-e1a6-4bf7-a703-f496b71e49db","dateUpdated":"2026-05-14T04:30:32.552Z"},"configurations":[{"lang":"en","supportingMedia":[{"base64":false,"type":"text/html","value":"<p>The application must expose an HTTP endpoint that calls <tt>cowboy_req:read_part/1,2</tt> to process <tt>multipart/form-data</tt> request bodies. 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":"Loïc Hoguin"}],"impacts":[{"capecId":"CAPEC-130","descriptions":[{"lang":"en","value":"CAPEC-130 Excessive Allocation"}]}],"source":{"discovery":"EXTERNAL"},"x_generator":{"engine":"cvelib 1.8.0"}},"adp":[{"title":"CISA ADP Vulnrichment","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"}}}],"providerMetadata":{"shortName":"CISA-ADP","orgId":"134c704f-9b21-4f2e-91b3-4a467353bcc0","dateUpdated":"2026-05-13T18:52:29.452Z"}}]}}}