Allocation of Resources Without Limits or Throttling Affecting cowboy package, versions >=2.0.0-pre.4 <2.18.0
Threat Intelligence
The probability is the direct output of the EPSS model, and conveys an overall sense of the threat of exploitation in the wild. The percentile measures the EPSS probability relative to all known EPSS scores. Note: This data is updated daily, relying on the latest available EPSS model version. Check out the EPSS documentation for more details.
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Test your applications- Snyk IDSNYK-HEX-COWBOY-18508173
- published2 Aug 2026
- disclosed28 Jul 2026
- creditQiyi Deng,Min Shi,Yongkang Xiao, Jing Chen
Introduced: 28 Jul 2026
NewCVE-2026-65624 (opens in a new tab)How to fix?
Upgrade cowboy to version 2.18.0 or higher.
Overview
Affected versions of this package are vulnerable to Allocation of Resources Without Limits or Throttling in the parse_header/3 and parse_hd_value/6 functions of cowboy_http in src/cowboy_http.erl, which enforce the max_headers limit by counting distinct header names rather than total header lines. An attacker can grow a connection process's binary memory to an arbitrary size, driving out-of-memory conditions, by sending many HTTP/1.1 header lines that share a single name, whose values are concatenated into one ever-growing binary under one map key that the max_headers cap never counts. Exploitation requires an HTTP/1.1 connection, and the growth is bounded by request_timeout (default 5 seconds) and any configured max_heap_size, so exhaustion depends on sustained abuse where max_heap_size is unset.
Workaround
This vulnerability can be avoided by configuring max_heap_size on the connection processes, which caps per-process memory so a single connection's concatenated header binary cannot exhaust host memory.