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Netty CVE-2026-55851

| EUVDEUVD-2026-46438 HIGH
Uncontrolled Resource Consumption (CWE-400)
2026-07-21 GitHub_M GHSA-q6cq-mhr2-jmr5
Denial Of Service Java Netty
8.7
CVSS 4.0 · Vendor: GitHub_M
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Severity by source

Vendor (GitHub_M) PRIMARY
8.7 HIGH
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/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X
vuln.today AI
7.5 HIGH

Network-reachable, unauthenticated, low-complexity trigger causing memory-exhaustion DoS; availability-only impact, so C:N/I:N/A:H with PR:N and UI:N.

3.1 AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
4.0 AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N
SUSE
7.5 HIGH
AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

Primary rating from Vendor (GitHub_M).

CVSS VectorVendor: GitHub_M

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/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X
Attack Vector
Network
Attack Complexity
Low
Privileges Required
None
User Interaction
None
Scope
X

Lifecycle Timeline

4
Patch available
Jul 21, 2026 - 23:36 EUVD
Source Code Evidence Fetched
Jul 21, 2026 - 22:05 vuln.today
Analysis Generated
Jul 21, 2026 - 22:05 vuln.today
CVE Published
Jul 21, 2026 - 21:22 cve.org
HIGH 8.7

Blast Radius

ecosystem impact
† from your stack dependencies † transitive graph · vuln.today resolves 4-path depth
  • 75 maven packages depend on io.netty:netty-codec-haproxy (3 direct, 72 indirect)

Ecosystem-wide dependent count for version 4.2.0.Final.

DescriptionCVE.org

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.

Articles & Coverage 1

News 6 New Java Vulnerabilities - 1 Critical, 5 High Severity Jul 22, 2026

AnalysisAI

Remote denial of service in the Netty networking framework (codec-haproxy module) versions 4.1.0.Final through 4.1.135 and 4.2.0.Final through 4.2.15.Final lets unauthenticated attackers exhaust JVM direct memory. The HAProxyMessageDecoder mis-parses a PROXY protocol v2 header whose version byte is 0xFF, sign-extending it to -1, which collides with the decoder's 'need more data' sentinel, so ByteToMessageDecoder accumulates inbound bytes in an unbounded cumulation buffer until the process runs out of direct memory. …

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Attack ChainAIDerived

Hypothetical attack flow derived from CVE metadata

Access
Reach PROXY-protocol-enabled Netty listener
Delivery
Send PROXY v2 prefix with version byte 0xFF
Exploit
Byte sign-extends to -1, hits need-more-data sentinel
Execution
Decoder buffers all inbound bytes in unbounded cumulation
Persist
Direct memory exhausted
Impact
Service crash or denial of service
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Vulnerability AssessmentAI

Exploitation The target application must use Netty's codec-haproxy module with HAProxyMessageDecoder in its channel pipeline and accept PROXY protocol v2 traffic from the attacker's network position - this is the concrete prerequisite. … Additional conditions and limiting factors are described in the full assessment.
Risk Assessment The supplied CVSS 4.0 vector (AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H) describes a network-reachable, low-complexity, unauthenticated attack whose only impact is availability, consistent with a resource-exhaustion DoS rather than code execution or data disclosure. … Full risk analysis with EPSS, KEV, and SSVC signal comparison available after sign-in.
Exploit Scenario An attacker connects over the network to a Netty-based service that accepts the HAProxy PROXY protocol and sends a PROXY v2 binary prefix whose version byte is 0xFF. The decoder treats the byte as -1, never completes parsing, and buffers all further bytes the attacker streams; by keeping the connection open and continuing to send data the attacker drives direct memory to exhaustion and crashes or stalls the service. …
Remediation Vendor-released patch: upgrade to Netty 4.1.136.Final (https://github.com/netty/netty/releases/tag/netty-4.1.136.Final) or 4.2.16.Final (https://github.com/netty/netty/releases/tag/netty-4.2.16.Final) per advisory GHSA-q6cq-mhr2-jmr5. … Detailed patch versions, workarounds, and compensating controls in full report.
Sign in to read full assessment

Recommended ActionAI

Within 24 hours: inventory all systems and applications using affected Netty versions, prioritizing production deployments. …

Sign in for detailed remediation steps and compensating controls.

Threat intelligence, references, and detailed analysis are available after sign-in.

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Vendor StatusVendor

SUSE

Severity: Important
Product Status
SUSE Linux Enterprise Desktop 15 SP7 Not-Affected
SUSE Linux Enterprise Desktop 15 SP7 Not-Affected
SUSE Linux Enterprise High Performance Computing 15 SP7 Not-Affected
SUSE Linux Enterprise High Performance Computing 15 SP7 Not-Affected
SUSE Linux Enterprise Module for Development Tools 15 SP7 Not-Affected

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CVE-2026-55851 vulnerability details – vuln.today
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