CVE-2023-34462 is a medium-severity (CVSS 6.5) Uncontrolled Resource Consumption vulnerability in io.netty:netty-handler. 1 public exploit or proof-of-concept reference is indexed, so weaponization risk is real. A fix is available for io.netty:netty-handler — see the affected versions and patch details below.
netty-handler SniHandler 16MB allocation
Exploitation Status
No confirmed exploitation observed yet
- CISA’s own triage has not observed active exploitation or public proof-of-concept code for this CVE as of its last assessment.
Exploitation and automatability from CISA’s SSVC triage for CVE-2023-34462.
EPSS Exploitation Probability
Probability of exploitation in the next 30 days, from FIRST.org EPSS.
How urgent is this, really
Where this sits among everything scored
Real-World Exposure
io.netty:netty-handlerReal-time download stats are indexed for npm and PyPI packages. This vulnerability affects Maven packages — download data is not available via public APIs for these ecosystems.
Description
Summary
The SniHandler can allocate up to 16MB of heap for each channel during the TLS handshake. When the handler or the channel does not have an idle timeout, it can be used to make a TCP server using the SniHandler to allocate 16MB of heap.
Details
The SniHandler class is a handler that waits for the TLS handshake to configure a SslHandler according to the indicated server name by the ClientHello record. For this matter it allocates a ByteBuf using the value defined in the ClientHello record.
Normally the value of the packet should be smaller than the handshake packet but there are not checks done here and the way the code is written, it is possible to craft a packet that makes the SslClientHelloHandler
1/ allocate a 16MB ByteBuf
2/ not fail decode method in buffer
3/ get out of the loop without an exception
The combination of this without the use of a timeout makes easy to connect to a TCP server and allocate 16MB of heap memory per connection.
Impact
If the user has no idle timeout handler configured it might be possible for a remote peer to send a client hello packet which lead the server to buffer up to 16MB of data per connection. This could lead to a OutOfMemoryError and so result in a DDOS.
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| ☕Maven | io.netty:netty-handler | all versions | 4.1.94.Finalio.netty:netty-handler:4.1.94.Final |
Affected Products
nettynettyResearch use only. For defensive security, authorized penetration testing, and academic research only. Never execute exploit code against systems without explicit written authorization.
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for io.netty:netty-handler, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update io.netty:netty-handler to 4.1.94.Final or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2023-34462 is resolved across your whole dependency graph.
Workarounds
Cap what an attacker can consume: apply request size, rate and timeout limits in front of the affected component, and run it with memory and CPU limits so exhaustion degrades one worker rather than the whole service.
Fixing This On Your OS
If you run this on a Linux distribution, patch through your package manager against the distro's own security advisory below — it tracks the exact backported fix for your release, which can ship on a different timeline (and sometimes a different severity) than the upstream project.
Configuration of SniHandler with an idle timeout will mitigate this issue.Source: Red Hat security advisory for CVE-2023-34462 (CC BY 4.0)
| Product | Fixed in | Advisory |
|---|---|---|
| Cryostat 2 on RHEL 8 | cryostat-tech-preview/cryostat-grafana-dashboard-rhel8:2.4.0-2 | RHSA-2023:7669 |
| Red Hat AMQ Broker 7 | netty | RHSA-2023:5946 |
| Red Hat AMQ Clients | netty | RHSA-2023:7697 |
| Red Hat AMQ Streams 2.5.0 | see advisory | RHSA-2023:5165 |
| Red Hat build of Quarkus 2.13.9 | netty-handler | RHSA-2023:7700 |
| Red Hat Data Grid 8.4.4 | netty | RHSA-2023:5396 |
| Red Hat JBoss Enterprise Application Platform | io.netty/netty-handler:4.1.94.Final-redhat-00001 | RHSA-2023:5488 |
| Red Hat JBoss Enterprise Application Platform 7.4 for RHEL 8 | eap7-netty-0:4.1.94-1.Final_redhat_00001.1.el8eap | RHSA-2023:5485 |
Frequently Asked Questions
Is CVE-2023-34462 in your dependencies?
Find it across Maven, including transitive dependencies.