{"id":"CVE-2026-8466","aliases":["AZL-88266","DEBIAN-CVE-2026-8466","EEF-CVE-2026-8466","EUVD-2026-30133","GHSA-jfc2-q6qh-g5x8","UBUNTU-CVE-2026-8466"],"status":"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) \u003e 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.","severity":{"version":"4.0","score":8.2,"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","level":"high","assessor":"cna","from":"cve"},"epss":{"day":"2026-11-09","score":0.00382,"percentile":0.32448,"model":"v2026.06.15"},"facts":{"in_kev":false,"known_exploited":false,"public_exploit":false,"fix_available":true},"cwes":["CWE-770"],"published":"2026-05-13T18:26:21Z","modified":"2026-11-05T05:40:51Z","fixes":[{"ecosystem":"Hex","package":"cowboy","fixed_in":["2.15.0"],"sources":["ghsa","osv"]},{"ecosystem":"Azure Linux:3","package":"rabbitmq-server","fixed_in":["3.13.7-5"],"sources":["osv"]},{"ecosystem":"Debian:14","package":"erlang-cowboy","fixed_in":["2.16.1+dfsg-1"],"sources":["osv"]}],"affected":[{"source":"ghsa","ecosystem":"Hex","package":"cowboy","ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"2.0.0"},{"fixed":"2.15.0"}]}]},{"source":"osv","ecosystem":"Azure Linux:3","package":"rabbitmq-server","ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"3.13.7-5"}]}]},{"source":"osv","ecosystem":"Debian:14","package":"erlang-cowboy","ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"2.16.1+dfsg-1"}]}],"versions":["0.10.0+dfsg1-1","0.6.1-1","0.6.1-2","0.6.1-3","0.6.1-4","0.8.6+dfsg-1","0.8.6+dfsg1-1","1.0.0+dfsg1-1","2.0.0~pre.1+dfsg1-1","2.0.0~pre.1+dfsg1-2","2.0.0~pre.1+dfsg1-3","2.0.0~pre.1+dfsg1-4"]},{"source":"osv","ecosystem":"Hex","package":"cowboy","ranges":[{"type":"SEMVER","events":[{"introduced":"2.0.0"},{"fixed":"2.15.0"}]}],"versions":["2.0.0","2.1.0","2.10.0","2.11.0","2.12.0","2.13.0","2.14.0","2.14.1","2.14.2","2.2.0","2.2.1","2.2.2","2.3.0","2.4.0","2.5.0","2.6.0","2.6.1","2.6.2","2.6.3","2.7.0","2.8.0","2.9.0"]},{"source":"osv","ecosystem":"Hex","package":"cowboy","ranges":[{"type":"SEMVER","events":[{"introduced":"2.0.0"},{"fixed":"2.15.0"}]}],"versions":["2.0.0","2.1.0","2.10.0","2.11.0","2.12.0","2.13.0","2.14.0","2.14.1","2.14.2","2.2.0","2.2.1","2.2.2","2.3.0","2.4.0","2.5.0","2.6.0","2.6.1","2.6.2","2.6.3","2.7.0","2.8.0","2.9.0"]},{"source":"osv","ecosystem":"Ubuntu:16.04:LTS","package":"erlang-cowboy","ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"}]}],"versions":["2.0.0~pre.1+dfsg1-1"]},{"source":"osv","ecosystem":"Ubuntu:18.04:LTS","package":"erlang-cowboy","ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"}]}],"versions":["2.0.0~pre.1+dfsg1-2"]},{"source":"osv","ecosystem":"Ubuntu:20.04:LTS","package":"erlang-cowboy","ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"}]}],"versions":["2.0.0~pre.1+dfsg1-4"]},{"source":"osv","ecosystem":"Ubuntu:22.04:LTS","package":"erlang-cowboy","ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"}]}],"versions":["2.0.0~pre.1+dfsg1-4"]},{"source":"osv","ecosystem":"Ubuntu:24.04:LTS","package":"erlang-cowboy","ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"}]}],"versions":["2.0.0~pre.1+dfsg1-4"]},{"source":"osv","ecosystem":"Ubuntu:25.10","package":"erlang-cowboy","ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"}]}],"versions":["2.0.0~pre.1+dfsg1-4"]},{"source":"osv","ecosystem":"Ubuntu:26.10","package":"erlang-cowboy","ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"}]}],"versions":["2.0.0~pre.1+dfsg1-4build1","2.18.0+dfsg-1"]},{"source":"osv","ecosystem":"Ubuntu:26.04:LTS","package":"erlang-cowboy","ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"}]}],"versions":["2.0.0~pre.1+dfsg1-4","2.0.0~pre.1+dfsg1-4build1"]}],"products":[{"vendor":"ninenines","product":"cowboy"}],"references":[{"url":"https://cna.erlef.org/cves/CVE-2026-8466.html","tags":["related","third-party-advisory","advisory","web","report"]},{"url":"https://osv.dev/vulnerability/EEF-CVE-2026-8466","tags":["related","web","report"]},{"url":"https://github.com/ninenines/cowboy/commit/5c6a2061b41bb5771c4659fac7d5a822dca5bafb","tags":["patch","fix","web","report"]},{"url":"https://nvd.nist.gov/vuln/detail/CVE-2026-8466","tags":["web","advisory"]},{"url":"https://github.com/advisories/GHSA-jfc2-q6qh-g5x8"},{"url":"https://github.com","tags":["web"]},{"url":"https://repo.hex.pm","tags":["web"]},{"url":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/8xxx/CVE-2026-8466.json","tags":["advisory"]},{"url":"https://github.com/ninenines/cowboy","tags":["package"]},{"url":"https://security-tracker.debian.org/tracker/CVE-2026-8466","tags":["advisory"]},{"url":"https://hex.pm/packages/cowboy","tags":["package"]},{"url":"https://ubuntu.com/security/CVE-2026-8466","tags":["report"]},{"url":"https://www.cve.org/CVERecord?id=CVE-2026-8466","tags":["report"]}],"sources":{"cve":[{"id":"CVE-2026-8466","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) \u003e 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.","status":"published","published":"2026-05-13T18:26:21.089Z","modified":"2026-05-14T04:30:32.552Z","cvss":[{"version":"4.0","score":8.2,"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","level":"high","assessor":"cna"}],"cwes":["CWE-770"],"updated_at":"2026-11-02T13:48:02.226896Z"}],"euvd":[{"id":"EUVD-2026-30133","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) \u003e 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.","status":"published","published":"2026-05-13T18:26:21Z","modified":"2026-05-14T04:30:32Z","cvss":[{"version":"4.0","score":8.2,"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","level":"high"}],"updated_at":"2026-11-02T19:04:31.993983Z"}],"ghsa":[{"id":"GHSA-jfc2-q6qh-g5x8","title":"Cowboy: 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) \u003e 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.","status":"published","published":"2026-05-13T21:32:06Z","modified":"2026-05-19T20:12:34Z","cvss":[{"version":"4.0","score":8.2,"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","level":"high"}],"cwes":["CWE-770"],"updated_at":"2026-11-02T14:40:12.430932Z"}],"nvd":[{"id":"CVE-2026-8466","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) \u003e 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.","status":"published","published":"2026-05-13T19:17:30.54Z","modified":"2026-10-26T14:10:00.13Z","cvss":[{"version":"4.0","score":8.2,"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/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","level":"high","assessor":"secondary"}],"cwes":["CWE-770"],"updated_at":"2026-11-02T14:12:19.020465Z"}],"osv":[{"id":"CVE-2026-8466","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) \u003e 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.","status":"published","published":"2026-05-13T18:26:21.089Z","modified":"2026-10-28T02:30:53.342322866Z","cvss":[{"version":"4.0","score":8.2,"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","level":"high"}],"cwes":["CWE-770"],"updated_at":"2026-11-02T15:45:18.482949Z"},{"id":"DEBIAN-CVE-2026-8466","description":"Allocation of Resources Without Limits or Throttling vulnerability in ninenines cowboy allows denial of service via unbounded buffer accumulation in multipart header parsing.  cowboy_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) \u003e 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.  This issue affects cowboy from 2.0.0 before 2.15.0.","status":"published","published":"2026-05-13T19:17:30.54Z","modified":"2026-10-27T09:47:29.667611196Z","cvss":[{"version":"4.0","score":8.2,"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/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","level":"high"}],"updated_at":"2026-11-02T15:46:05.022702Z"},{"id":"EEF-CVE-2026-8466","title":"Unbounded buffer accumulation in multipart header parsing causes denial of service in cowboy","description":"## Summary\n\nAllocation 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) \u003e 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.\n\n## Configurations\n\nThe 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.","status":"published","published":"2026-05-13T18:26:21.089Z","modified":"2026-09-08T03:45:10.616655234Z","cvss":[{"version":"4.0","score":8.2,"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","level":"high"}],"cwes":["CWE-770"],"updated_at":"2026-11-02T15:46:33.520522Z"},{"id":"GHSA-jfc2-q6qh-g5x8","title":"Cowboy: 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) \u003e 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.","status":"published","published":"2026-05-13T21:32:06Z","modified":"2026-05-19T20:26:06.334145132Z","cvss":[{"version":"4.0","score":8.2,"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","level":"high"}],"cwes":["CWE-770"],"updated_at":"2026-11-02T15:46:50.336262Z"},{"id":"UBUNTU-CVE-2026-8466","description":"Allocation of Resources Without Limits or Throttling vulnerability in ninenines cowboy allows denial of service via unbounded buffer accumulation in multipart header parsing. cowboy_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) \u003e 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. This issue affects cowboy from 2.0.0 before 2.15.0.","status":"published","published":"2026-05-13T19:17:00Z","modified":"2026-10-17T13:01:12.738179152Z","cvss":[{"version":"4.0","score":8.2,"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","level":"high"}],"updated_at":"2026-11-02T16:57:24.828975Z"},{"id":"AZL-88266","title":"CVE-2026-8466 affecting package rabbitmq-server for versions less than 3.13.7-5","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) \u003e 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.","status":"published","published":"2026-05-13T19:17:30Z","modified":"2026-11-05T05:40:51Z","updated_at":"2026-11-05T16:41:25.436971Z"}]}}