CVE-2026-65624

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.