erlang-cowboy — security advisory
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) > 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.
- Products
- erlang-cowboy
- Affected versions
- 2.0.0~pre.1+dfsg1-1, 2.0.0~pre.1+dfsg1-2, 2.0.0~pre.1+dfsg1-4, 2.0.0~pre.1+dfsg1-4build1, 2.18.0+dfsg-1
- Fixed versions
- Not specified
- CVEs
- CVE-2026-8466
- Confirmed fixed CVEs
- Not specified
- Updated in this feed
- 31 Oct 2026, 03:23 UTC · Revision 1
Source evidence
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) > 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.
osv:UBUNTU-CVE-2026-8466
erlang-cowboy
Fixed versions: Not specified
erlang-cowboy
Fixed versions: Not specified
erlang-cowboy
Fixed versions: Not specified
erlang-cowboy
Fixed versions: Not specified
erlang-cowboy
Fixed versions: Not specified
erlang-cowboy
Fixed versions: Not specified
erlang-cowboy
Fixed versions: Not specified
erlang-cowboy
Fixed versions: Not specified
Complete source record
{
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"url": "https://osv.dev/vulnerability/UBUNTU-CVE-2026-8466",
"method": "structured",
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"summary": "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) > 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.",
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],
"modified": "2026-10-17T13:01:12.738179152Z",
"provider": "osv",
"upstream": [
"CVE-2026-8466"
],
"references": [
"https://ubuntu.com/security/CVE-2026-8466",
"https://www.cve.org/CVERecord?id=CVE-2026-8466",
"https://cna.erlef.org/cves/CVE-2026-8466.html",
"https://osv.dev/vulnerability/EEF-CVE-2026-8466",
"https://github.com/ninenines/cowboy/commit/5c6a2061b41bb5771c4659fac7d5a822dca5bafb"
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"security_relevant": true,
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},
"source_id": "core-osv",
"document_id": 361251,
"published_at": "2026-05-13T19:17:00+00:00"
}