High [CVE-2026-56819] Denial of Service via HTTP/2 DATA frame memory leak

Netty is a network application framework for development of protocol servers and clients. In versions 4.2.0.Final through 4.2.15.Final and 4.1.0.Final through 4.1.135.Final, a remote unauthenticated peer can leak one direct `ByteBuf` per HTTP/2 `DATA` frame in applications that enable HTTP/2 content decompression via `DelegatingDecompressorFrameListener`.

When a `DATA` frame is processed for a stream whose decompressor has already been closed, `Http2Decompressor.decompress(...)` calls `decompressor.writeInbound(data.retain())` and does not release the retained buffer on the error path, eventually exhausting direct memory and crashing the JVM. This issue is fixed in versions 4.1.136.Final and 4.2.16.Final.

A remote, unauthenticated attacker can exploit this vulnerability by sending specially crafted HTTP/2 DATA frames to applications that use Netty and have HTTP/2 content decompression enabled. This can lead to memory exhaustion, causing the application to crash and resulting in a Denial of Service (DoS).

This is an Important vulnerability in Netty's HTTP/2 codec, which could lead to a denial of service. Red Hat products utilizing netty-codec-http2 with HTTP/2 content decompression enabled are susceptible to memory exhaustion when processing specially crafted HTTP/2 DATA frames.