Copyright © 2012 Red Hat, Inc. All rights reserved. Important 2026-07-28T10:01:01 cowboy: Cowboy: Denial of Service via HTTP/1.1 duplicate header names 7.5 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H CWE-1050

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.

A flaw was found in Cowboy. An unauthenticated remote attacker can exploit this vulnerability by sending multiple HTTP/1.1 header lines with the same name. This bypasses the `max_headers` limit, causing the connection process memory to grow uncontrollably. This can lead to memory exhaustion and a Denial of Service (DoS) condition in the Erlang Virtual Machine (VM).

This Important vulnerability allows an unauthenticated remote attacker to cause a denial of service by sending crafted HTTP/1.1 requests with duplicate header names. The `cowboy` library, utilized by components such as `rabbitmq-server` in Red Hat Hardened Images, fails to properly limit memory consumption from concatenated header values. This can lead to memory exhaustion of the Erlang Virtual Machine, impacting service availability, particularly if the `max_heap_size` is not explicitly configured. Mitigation for this issue is either not available or the currently available options do not meet the Red Hat Product Security criteria comprising ease of use and deployment, applicability to widespread installation base or stability. Red Hat Hardened Images 2026-07-28T00:00:00Z RHSA-2026:47231 rabbitmq-server4-3-main-4.3.4-0.2.hum1 Red Hat Hardened Images 2026-07-28T00:00:00Z RHSA-2026:47236 rabbitmq-server4-2-main-4.2.9-0.2.hum1 https://www.cve.org/CVERecord?id=CVE-2026-65624 https://nvd.nist.gov/vuln/detail/CVE-2026-65624 https://cna.erlef.org/cves/CVE-2026-65624.html https://github.com/ninenines/cowboy/commit/3a34d8c1cfd94326466aa16a9017236691dc9c55 https://osv.dev/vulnerability/EEF-CVE-2026-65624