Weakness Type (CWE)

CWE-770 — CWE-770 Allocation of Resources Without Limits or Throttling

CAPEC

CVSS 4.0 Score

6.9

MEDIUM

CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:L/SC:N/SI:N/SA:N

Vulnerability description

Allocation of Resources Without Limits or Throttling vulnerability in ninenines cowboy allows an unauthenticated remote attacker to exhaust connection process memory over HTTP/1.1.

The HTTP/1.1 handler in cowboy_http enforces the max_headers limit by counting the number of distinct header names in a map (maps:size(Headers)). When a request contains multiple header lines with the same name, the values are concatenated into a single ever-growing binary stored under that one map key (", " for regular headers, "; " for cookies), so the map size stays at one and the max_headers cap (default 100) is never reached. Because no accumulator bounds the total number of header lines or the total byte size of the header block (only per-line max_header_name_length and max_header_value_length apply), an unauthenticated client can send an arbitrary number of header lines with the same name and grow the connection process's binary memory to arbitrary size within the request window.

The impact per connection is bounded by request_timeout (default 5 seconds, not reset by header data), and by max_heap_size when set (the offending connection process is killed once its heap grows past the limit). When max_heap_size is left at the default (unset), sustained abuse can drive the Erlang VM into out-of-memory conditions.

This issue affects cowboy from 2.0.0-pre.4 before 2.18.0.

Affected

pkg:hex/cowboy

Module Source File Routine
cowboy_http src/cowboy_http.erl cowboy_http:parse_header/3
cowboy_http:parse_hd_value/6
Status Type Version Changes / Fixed in
affected semver ⓘ 2.0.0-pre.4 < 2.18.0

pkg:github/ninenines/cowboy

Module Source File Routine
cowboy_http src/cowboy_http.erl cowboy_http:parse_header/3
cowboy_http:parse_hd_value/6
Status Type Version Changes / Fixed in
affected git ⓘ 309780a9fd < 3a34d8c1cf

References

Credits

  • Finder: Qiyi Deng / Wuhan University
  • Finder: Min Shi / Wuhan University
  • Finder: Yongkang Xiao / Wuhan University
  • Finder: Jing Chen / Wuhan University
  • Remediation developer: Loïc Hoguin
  • Analyst: Jonatan Männchen / EEF

CVE record as JSON:  GET /cves/CVE-2026-65624.json
OSV record as JSON:  GET /osv/EEF-CVE-2026-65624.json