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CVE-2026-42587

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

CVSS 7.5 HIGHEPSS 0.5%CWE-400
In short

Netty's decompression feature has a safety limit to prevent 'decompression bombs' (malicious compressed files that explode into huge sizes), but this limit is ignored when using certain compression types like Brotli, zstd, or Snappy. An attacker can exploit this to crash a server by sending specially crafted compressed data that consumes all available memory.

Technical detail

HttpContentDecompressor in Netty fails to enforce the maxAllocation limit for Brotli, zstd, and Snappy content encodings, while correctly enforcing it for gzip and deflate via ZlibDecoder. An attacker can send a compressed payload with Content-Encoding: br/zstd/snappy to trigger unbounded memory allocation, causing out-of-memory DoS. The same bypass affects DelegatingDecompressorFrameListener in HTTP/2 connections.

Summary generated and translated by AI from the official description.
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.
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
Affected products
io.netty · netty-codec-httpio.netty · netty-codec-http2netty · netty

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References
https://github.com/netty/netty/security/advisories/GHSA-f6hv-jmp6-3vwv