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High severity7.5OSV Advisory· Published Jul 21, 2026· Updated Jul 30, 2026

CVE-2026-55851

CVE-2026-55851

Description

Netty is a network application framework for development of protocol servers and clients. In versions 4.2.0.Final up to (but not including) 4.2.16.Final, and 4.1.0.Final up to (but not including) 4.1.135, the HAProxyMessageDecoder in Netty's codec-haproxy module performs protocol version detection by reading the 13th byte as a signed Java byte and widening it to int without masking; a PROXY protocol v2 binary prefix followed by version byte 0xFF sign-extends to -1, collides with the decoder's need-more-data sentinel, and causes ByteToMessageDecoder to accumulate inbound bytes in an unbounded cumulation buffer until direct memory is exhausted. This issue is fixed in versions 4.1.136.Final and 4.2.16.Final.

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Affected packages

Versions sourced from the GitHub Security Advisory.

PackageAffected versionsPatched versions
io.netty:netty-codec-haproxyMaven
>= 4.2.0.Final, < 4.2.16.Final4.2.16.Final
io.netty:netty-codec-haproxyMaven
>= 4.1.0.Final, < 4.1.136.Final4.1.136.Final

Affected products

81

Patches

Vulnerability mechanics

References

7

News mentions

1