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) > 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.

Weaknesses 1

References 3

• cna.erlef.org https://cna.erlef.org/cves/CVE-2026-8466.html
• github.com https://github.com/ninenines/cowboy/commit/5c6a2061b41bb5771c4659fac7d5a822dca5bafb
• osv.dev https://osv.dev/vulnerability/EEF-CVE-2026-8466

Remediation