CVE-2023-34462 is a medium-severity (CVSS 6.5) Uncontrolled Resource Consumption vulnerability in io.netty:netty-handler. 1 public exploit reference exists, 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
EPSS (Exploit Prediction Scoring System) is a daily probability model maintained by FIRST.org. It estimates the likelihood a CVE will be exploited in production environments within the next 30 days, derived from real-world threat intelligence signals.
How urgent is this, really
CVE-2023-34462 plotted by exploitation likelihood (EPSS) against impact (CVSS). The shaded corner — EPSS 50%+ and CVSS 7.0+ — is where this CVE doesn't sit, though severity or exploitability alone can still warrant action.
Where this sits among everything scored
Of 377,636 CVEs with a current EPSS score, this one falls in the < 10% band (highlighted). Real counts from FIRST.org, not a sample — log-scaled since the landscape is heavily right-skewed.
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 |
Research 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
If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.
How O3 protects you
O3 Security's impact-aware SCA analyses which vulnerable code paths your application actually calls, so a match like CVE-2023-34462 can be triaged on real exposure rather than presence alone.
Tailored to CVE-2023-34462. Runtime protection reduces exposure until a permanent patch is applied and verified — it complements patching, it doesn't replace it.
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.
| 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.Final | io.netty/netty-handler:4.1.100.Final-redhat-00001 | RHSA-2023:7700 |
| Red Hat Data Grid 8.4.4 | netty | RHSA-2023:5396 |
| Red Hat JBoss Enterprise Application Platform 7 | netty | 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?
O3 Security finds CVE-2023-34462 across Maven dependencies, including transitive ones, and its impact-aware SCA ranks findings by whether your code actually calls the vulnerable path.