CVE-2026-55851: Netty [codec-haproxy] Signed-Byte Sentinel Collision Vulnerability
HIGHCVE-2026-55851 is a HIGH [codec-haproxy] signed-byte sentinel collision vulnerability (CWE-400: Uncontrolled Resource Consumption) affecting Netty libraries in the Maven ecosystem. The issue involves [codec-haproxy] signed-byte sentinel collision in haproxymessagedecoder leads to unbounded memory exhaustion. Remediation is available by upgrading affected packages to version 4.2.16.Final, 4.1.136.Final.
CVE-2026-55851 at a Glance
How to Fix CVE-2026-55851
To remediate this vulnerability, upgrade all affected Netty dependencies to a patched release. Both direct and transitive dependencies should be checked, as frameworks or security libraries may pull in vulnerable versions transitively.
<dependency>
<groupId>io.netty</groupId>
<artifactId>netty-codec-haproxy</artifactId>
<version>4.2.16.Final</version>
</dependency><dependency>
<groupId>io.netty</groupId>
<artifactId>netty-codec-haproxy</artifactId>
<version>4.1.136.Final</version>
</dependency>Run the following command in your project directory to verify that all resolved dependencies use the patched release:
mvn dependency:tree -Dincludes=io.nettyHow to Check if You Are Affected
To determine whether your Java application is affected by CVE-2026-55851, inspect your build dependencies using the Maven Dependency Plugin:
mvn dependency:tree -Dincludes=io.nettyAnalyze the terminal output to locate any version of Netty in your dependency tree. If any resolved version matches the vulnerable ranges listed in the table below (for example, versions earlier than 4.2.16.Final), your application is affected.
Note: The mvn dependency:tree -Dincludes=io.netty command inspects the resolved dependency graph declared in your project's POM files; it does not perform automated security scanning or inspect runtime dynamic classpaths. Always verify runtime container classpaths and shaded JARs.
Technical Details
Vulnerability Mechanism & Technical Analysis
This vulnerability is classified under CWE-400: Uncontrolled Resource Consumption, where the product does not properly control the allocation and maintenance of a limited resource. In Netty, software state validation or input boundaries are circumvented during processing. Review the official source advisory statement below for specific affected components, classes, and reproduction details.
Source Advisory Statement
CVE-2026-55851 Affected Netty Versions
2 component(s)| Product / Package | Ecosystem | Affected Versions | Fixed Version |
|---|---|---|---|
|
io.netty:netty-codec-haproxy
|
Maven |
≥ 4.2.0.Final
< 4.2.16.Final
|
4.2.16.Final
|
|
io.netty:netty-codec-haproxy
|
Maven |
≥ 4.1.0.Final
< 4.1.136.Final
|
4.1.136.Final
|
References
Frequently Asked Questions
What is CVE-2026-55851?
Which Netty versions are affected?
What version fixes CVE-2026-55851?
Is netty-codec-haproxy affected?
What CWE is associated with CVE-2026-55851?
How can I check Maven dependencies for CVE-2026-55851?
Machine-readable OSV JSON
OSV v1.5 Schema
{
"schema_version" : "1.4.0",
"id" : "GHSA-q6cq-mhr2-jmr5",
"modified" : "2026-07-22T21:23:25Z",
"published" : "2026-07-22T21:23:25Z",
"aliases" : [ "CVE-2026-55851" ],
"summary" : "Netty: [codec-haproxy] Signed-Byte Sentinel Collision in HAProxyMessageDecoder Leads to Unbounded Memory Exhaustion",
"details" : "The `HAProxyMessageDecoder` in netty's `codec-haproxy` module performs protocol version detection by reading the 13th byte of the inbound stream as a signed Java `byte` and widening it to `int` without masking. When an attacker sends a PROXY protocol v2 binary prefix (`0D 0A 0D 0A 00 0D 0A 51 55 49 54 0A`) followed by version byte `0xFF`, the sign extension produces `-1`, which collides with the decoder's \"need more data\" sentinel value. This collision traps the decoder in a version-detection loop where it perpetually requests more data without consuming any bytes, never instantiates the `HeaderExtractor` that enforces header size limits, and causes `ByteToMessageDecoder` to accumulate all subsequent inbound bytes into an unbounded `cumulation` buffer until the JVM exhausts its direct memory allocation.",
"severity" : [ {
"type" : "CVSS_V4",
"score" : "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"
} ],
"affected" : [ {
"package" : {
"ecosystem" : "Maven",
"name" : "io.netty:netty-codec-haproxy"
},
"ranges" : [ {
"type" : "ECOSYSTEM",
"events" : [ {
"introduced" : "4.2.0.Final"
}, {
"fixed" : "4.2.16.Final"
} ]
} ],
"database_specific" : {
"last_known_affected_version_range" : "<= 4.2.15.Final"
}
}, {
"package" : {
"ecosystem" : "Maven",
"name" : "io.netty:netty-codec-haproxy"
},
"ranges" : [ {
"type" : "ECOSYSTEM",
"events" : [ {
"introduced" : "4.1.0.Final"
}, {
"fixed" : "4.1.136.Final"
} ]
} ],
"database_specific" : {
"last_known_affected_version_range" : "<= 4.1.135.Final"
}
} ],
"references" : [ {
"type" : "WEB",
"url" : "https://github.com/netty/netty/security/advisories/GHSA-q6cq-mhr2-jmr5"
}, {
"type" : "ADVISORY",
"url" : "https://nvd.nist.gov/vuln/detail/CVE-2026-55851"
}, {
"type" : "WEB",
"url" : "https://github.com/netty/netty/commit/5b68c61f37aa4a3045cba624cbea239655c9003b"
}, {
"type" : "WEB",
"url" : "https://github.com/netty/netty/commit/bb2ff68a1fb71cb4b0eb9a9e17b66c52aff680c6"
}, {
"type" : "PACKAGE",
"url" : "https://github.com/netty/netty"
}, {
"type" : "WEB",
"url" : "https://github.com/netty/netty/releases/tag/netty-4.1.136.Final"
}, {
"type" : "WEB",
"url" : "https://github.com/netty/netty/releases/tag/netty-4.2.16.Final"
} ],
"database_specific" : {
"cwe_ids" : [ "CWE-400" ],
"severity" : "HIGH",
"github_reviewed" : true,
"github_reviewed_at" : "2026-07-22T21:23:25Z",
"nvd_published_at" : "2026-07-21T22:17:14Z"
}
}