Infinite loop in Netty - CVE-2026-55851

Vulnerability identifier: #VU137569

CSH Severity: Medium

CVSS v4: 8.7 [CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N]

CVE-ID: CVE-2026-55851

CWE-ID: CWE-835

Exploitation vector: Remote access

Exploit availability: No public exploit available

The vulnerability allows a remote attacker to cause a denial of service.

The vulnerability exists due to improper handling of a signed-byte sentinel collision in HAProxyMessageDecoder when processing a crafted PROXY protocol v2 header. A remote attacker can send a specially crafted PROXY protocol v2 prefix followed by a version byte of 0xff to cause a denial of service.

The issue can trap version detection in a loop that prevents header size limits from being enforced and causes inbound bytes to accumulate in an unbounded buffer until direct memory is exhausted.

Netty
SUSE Linux Enterprise Server 15 SP6
SUSE Linux Enterprise Server 15 SP5
SUSE Linux Enterprise Server 15 SP4
SUSE Linux Enterprise Server for SAP Applications 15
SUSE Linux Enterprise High Performance Computing 15
SUSE Linux Enterprise High Performance Computing ESPOS 15
SUSE Linux Enterprise High Performance Computing LTSS 15
SUSE Linux Enterprise Server 15
SUSE Linux Enterprise Desktop 15
SUSE Linux Enterprise Real Time 15
Development Tools Module
SUSE Package Hub 15
netty-tcnative-debugsource
netty-tcnative
netty
netty-javadoc

Install security update from vendor's website.

Netty - addressed in versions 4.1.136, 4.2.16
netty-tcnative-debugsource - update to 2.0.80-150200.3.48.1
netty-tcnative - update to 2.0.80-150200.3.48.1
netty - update to 4.1.136-150200.4.53.1
netty-javadoc - update to 4.1.136-150200.4.53.1

• https://github.com/netty/netty/security/advisories/GHSA-q6cq-mhr2-jmr5

• Multiple vulnerabilities in Netty
• SUSE update for netty, netty-tcnative