Netty: 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… (CVE-2026-55851)
Description
A vulnerability in the HAProxyMessageDecoder component of the Netty codec-haproxy module causes an infinite loop due to a signed-byte sentinel collision during protocol version detection. This occurs when the 13th byte of the inbound stream is 0xFF, leading to unbounded memory growth and eventual JVM memory exhaustion. The issue affects Netty versions 4.2.0.Final up to but not including 4.2.16.Final, and 4.1.0.Final up to but not including 4.1.136.Final.
CVSS v3.1
Score 7.5high
Affected software
pkg:deb/ubuntu/netty?arch=source&distro=esm-infra-legacy/trustypkg:deb/ubuntu/netty?arch=source&distro=esm-apps-legacy/xenialpkg:deb/ubuntu/netty?arch=source&distro=esm-apps/bionicpkg:deb/ubuntu/netty?arch=source&distro=esm-apps/focalpkg:deb/ubuntu/netty?arch=source&distro=esm-apps/jammypkg:deb/ubuntu/netty?arch=source&distro=esm-apps/noblepkg:deb/ubuntu/netty?arch=source&distro=stonkingpkg:deb/ubuntu/netty?arch=source&distro=esm-apps/resoluteRun on your own infrastructure? Check whether these packages are installed with threat-finder — our free open-source scanner.
Weaknesses
AI-Powered Analysis
Machine-generated threat intelligence
Technical Analysis
CVE-2026-55851 is a denial-of-service vulnerability in the HAProxyMessageDecoder of the Netty codec-haproxy module. The vulnerability arises from a signed-byte sentinel collision during protocol version detection, where the decoder interprets the 13th byte of the inbound stream as 0xFF, which sign-extends to -1. This matches the sentinel value indicating 'need more data', causing the decoder to enter an infinite loop requesting more data without consuming any bytes. This results in unbounded memory growth and eventual exhaustion of JVM memory resources. The affected versions are Netty 4.2.0.Final up to but excluding 4.2.16.Final, and 4.1.0.Final up to but excluding 4.1.136.Final.
Potential Impact
The vulnerability leads to a denial-of-service condition by causing unbounded memory growth and eventual JVM memory exhaustion. There is no impact on confidentiality or integrity, only availability is affected.
Mitigation Recommendations
A fix is available in Netty versions 4.2.16.Final and 4.1.136.Final and later. Users should upgrade to these or later versions to remediate the issue. No vendor advisory content was provided to indicate alternative mitigations or temporary fixes.
Technical Details
- Gcve Source
- db.gcve.eu
- Osv Id
- GHSA-q6cq-mhr2-jmr5
- Osv Schema Version
- 1.4.0
- Aliases
- ["CVE-2026-55851"]
- Ecosystems
- ["Maven"]
- Database Specific Severity
- HIGH
- Cvss Version
- 4.0
Threat ID: 6a6150e99c2644c7f8da2339
Added to database: 07/22/2026, 23:23:21 UTC
Last enriched: 10/18/2026, 04:49:31 UTC
Last updated: 10/21/2026, 13:20:22 UTC
Views: 85
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