CVE-2026-42587 — Netty: HttpContentDecompressor maxAllocation bypass via Content-Encoding: br/zstd/snappy enables decompression bomb DoS

2026-10-07T16:46:35.045065+00:00

Affected: netty, io.netty netty-codec-http, io.netty netty-codec-http2, Red Hat Cryostat 4 on RHEL 9, Red Hat AMQ Broker 7.13.6, Red Hat AMQ Broker 7.14.1, Red Hat build of Apache Camel 4.18.1.P1 for Spring Boot 3.5.16, Red Hat build of Quarkus 3.27.4, Red Hat build of Quarkus 3.33.2, Red Hat Data Grid 8.6.2 and 30 more

Netty is an asynchronous, event-driven network application framework. Prior to 4.2.13.Final and 4.1.133.Final, HttpContentDecompressor accepts a maxAllocation parameter to limit decompression buffer size and prevent decompression bomb attacks. This limit is correctly enforced for gzip and deflate encodings via ZlibDecoder, but is silently ignored when the content encoding is br (Brotli), zstd, or snappy. An attacker can bypass the configured decompression limit by sending a compressed payload with Content-Encoding: br instead of Content-Encoding: gzip, causing unbounded memory allocation and out-of-memory denial of service. The same vulnerability exists in DelegatingDecompressorFrameListener for HTTP/2 connections. This vulnerability is fixed in 4.2.13.Final and 4.1.133.Final.

GHSA-563q-j3cm-6jxm — Netty susceptible to HTTP/2 Reset Attack with different on-the-wire signature

2026-10-07T16:46:35.045243+00:00

Affected: Maven: io.netty:netty-codec-http2

### Summary

Netty HTTP/2 max header size handling produces attack similar to HTTP/2 Rapid Reset.

### Details

There is a setting in the http2 specification called `SETTINGS_MAX_HEADER_LIST_SIZE`. According to[ the RFC](https://www.rfc-editor.org/rfc/rfc9113.html#name-defined-settings): “This advisory setting informs a peer of the maximum field section size that the sender is prepared to accept, in units of octets.”

When a client sends that setting to Netty, it appears that Netty will behave as follows:

- Read the request - Proxy the request to the origin - Attempt to produce a response - Create an exception while writing the headers for the response

Functionally, this should be similar to the http2 reset attack, but with a different on-the-wire signature.

## Remediation

When speaking with clients, Netty should potentially treat this as “advisory” and ignore it. It would be best to ignore the SETTINGS_MAX_HEADER_LIST_SIZE setting from clients (or ignore it when sending to clients). According to the spec, a server does not need to honor this advisory setting, and it appears that other http/2 implementations ignore it when acting as a server.

### Impact

This is a DDoS attack similar to the HTTP/2 Rapid Reset Attack.

## Credit Jonathan Looney (Engineering, Netflix)

## Contact Ashley Tolbert (Security, Netflix) - artolbert@netflix.com

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CVE-2026-42587 — Netty: HttpContentDecompressor maxAllocation bypass via Content-Encoding: br/zstd/snappy enables decompression bomb DoS

GHSA-563q-j3cm-6jxm — Netty susceptible to HTTP/2 Reset Attack with different on-the-wire signature