CVE-2023-34462Network attack vector

Denial of service via oversized ClientHello

Published Jun 22, 2023 · Updated Feb 13, 2025

Allocation flaw in Netty before 4.1.94.Final allows remote authenticated users to cause denial of service via crafted TLS ClientHello. SniHandler trusts a length from the ClientHello and allocates a ByteBuf up to 16MB for each channel without enforcing a maximum or requiring an idle timeout. A remote authenticated user can open repeated handshakes to exhaust JVM heap and trigger OutOfMemoryError, interrupting the service.

CVSS severity6.5
Medium
EPSS probability2.46%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Allocation flaw in Netty before 4.1.94.Final allows remote authenticated users to cause denial of service via crafted TLS ClientHello. SniHandler trusts a length from the ClientHello and allocates a ByteBuf up to 16MB for each channel without enforcing a maximum or requiring an idle timeout. A remote authenticated user can open repeated handshakes to exhaust JVM heap and trigger OutOfMemoryError, interrupting the service.

The record

CVE
CVE-2023-34462
Published
Jun 22, 2023
Updated
Feb 13, 2025
Vendor
The Netty Project
Product
Netty
Classifications
CWE-400, T1499.004
Attack vector
network
Privileges
authenticated

Timeline

How it unfolded

  1. Jun 22, 2023CVE publishedPublication date reported by the CVE source.
  2. Feb 13, 2025Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=< 4.1.94.Final

What conditions does exploitation require?

Attack vectornetwork
Required privilegesauthenticated

What is affected?

The Netty Project · Nettyversion=< 4.1.94.Final

Published CVSS scores

6.5GitHub Advisory DatabaseCVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

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No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-400Uncontrolled Resource Consumption
T1499.004Endpoint Denial of Service: Application or System Exploitation

Public exploit references

No public exploit references are available in this record.

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Technologies

Your stack

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Your stack

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