CVE-2026-55851: 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

unknownCVE-2026-55851

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.

Details

Source: NVD Recent CVEs (US · database · site)
Severity: unknown
Published: 2026-07-21
Last updated: 2026-07-23
Exploitation: Not in CISA KEV at last sync

Original advisory: https://nvd.nist.gov/vuln/detail/CVE-2026-55851

Exploitation outlook

EPSS (FIRST.org) estimates each CVE’s probability of exploitation in the next 30 days — here is the CSIRTS.com read on those numbers.

Low exploitation riskCVE-2026-558510.61% 30-day exploitation probability — currently an unlikely target, but scores change as exploit code circulates. Riskier than 46% of all scored CVEs.

Referenced CVEs

CVE	CSIRTS overview	External
CVE-2026-55851	coverage & exploitation status	NVD · CVE.org

Same CVEs, other sources

How other CERTs, PSIRTs and databases cover the vulnerabilities in this advisory.

CVE-2026-55851: 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

Details

Exploitation outlook

Referenced CVEs

Same CVEs, other sources

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