CVE-2026-59899: Netty HttpContentEncoder: Unbounded Per-Connection Queue Growth via HTTP/1.1 Pipelining Leads to Denial of Service

Netty is a network application framework for development of protocol servers and clients. Prior to 4.1.136.Final, the HTTP decoder in netty-codec-http fails to properly limit decompression of HTTP body content encoded with gzip or other compression algorithms. An attacker can send HTTP requests with highly compressed payloads that decompress to enormous sizes, causing memory exhaustion and denial of service. This issue is fixed in versions 4.1.136.Final and later.

— Red Hat

Netty is an asynchronous, event-driven network application framework. Prior to versions 4.1.136.Final and 4.2.16.Final, HttpContentEncoder (the superclass of the production handler HttpContentCompressor) maintains a per-channel ArrayDeque<CharSequence> named acceptEncodingQueue that accumulates attacker-controlled data without any size limit. The queue is filled on the I/O thread for every inbound HTTP request and drained only when the application later writes a non-1xx response. This creates a resource exhaustion vulnerability when an attacker exploits HTTP/1.1 pipelining to flood the connection with requests faster than the application produces responses. This issue has been fixed in versions 4.1.136.Final and 4.2.16.Final.

— MITRE