CVE-2026-55851
Severity CVSS v4.0:
HIGH
Type:
CWE-400
Uncontrolled Resource Consumption ('Resource Exhaustion')
Publication date:
21/07/2026
Last modified:
30/07/2026
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.
Impact
Base Score 4.0
8.70
Severity 4.0
HIGH
Base Score 3.x
7.50
Severity 3.x
HIGH
Vulnerable products and versions
| CPE | From | Up to |
|---|---|---|
| cpe:2.3:a:netty:netty:*:*:*:*:*:*:*:* | 4.1.0 (including) | 4.1.136 (excluding) |
| cpe:2.3:a:netty:netty:*:*:*:*:*:*:*:* | 4.2.0 (including) | 4.2.16 (excluding) |
To consult the complete list of CPE names with products and versions, see this page
References to Advisories, Solutions, and Tools
- https://github.com/netty/netty/commit/5b68c61f37aa4a3045cba624cbea239655c9003b
- https://github.com/netty/netty/commit/bb2ff68a1fb71cb4b0eb9a9e17b66c52aff680c6
- https://github.com/netty/netty/releases/tag/netty-4.1.136.Final
- https://github.com/netty/netty/releases/tag/netty-4.2.16.Final
- https://github.com/netty/netty/security/advisories/GHSA-q6cq-mhr2-jmr5