CVE-2026-55851 Details
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.
A denial-of-service vulnerability has been identified in Netty's HAProxy codec module, specifically in versions 4.2.0.Final prior to 4.2.16.Final and 4.1.0.Final prior to 4.1.135. The issue arises in the HAProxyMessageDecoder, which improperly handles protocol version detection by reading the 13th byte as a signed value. This misinterpretation allows an attacker to send a PROXY protocol v2 binary prefix followed by a version byte of 0xFF, causing the decoder to enter an infinite loop of data requests. As a result, the decoder fails to process incoming bytes correctly, leading to an unbounded accumulation of data in the 'cumulation' buffer. This unchecked growth continues until the JVM runs out of direct memory, causing a crash.
Users can upgrade to Netty versions 4.1.136.Final or 4.2.16.Final to address this vulnerability.
Metrics
CVSS 4.0 Severity and Vector Strings:
CVSS 3.x Severity and Vector Strings:
No data available for CVSS Version 2.0 on this CVE.
CISA-ADP
Assessed Jul 23, 2026References to Advisories, Solutions, and Tools
By selecting these links, you will be leaving this site. These are references gathered from the official CVE record and are not endorsed by Volerion.
Weakness Enumeration
| CWE-ID | CWE Name | Source |
|---|---|---|
| CWE-400 | Uncontrolled Resource Consumption | [email protected] |
Affected Products
| Product | Versions |
|---|---|
| netty netty | >= 4.1.0, < 4.1.136 >= 4.2.0, < 4.2.16 |
CPE
Remediation
| |
Change History
3 change records found show changes
| Date | Action | Recorded By |
|---|---|---|
| Jul 30, 2026 | Initial Analysis | [email protected] |
| Jul 23, 2026 | CVE Modified | CISA-ADP |
| Jul 21, 2026 | New CVE Received | [email protected] |