CVE-2023-34462 netty-handler SniHandler 16MB allocation
Attackers can cause excessive memory allocation in Netty's SniHandler during TLS handshakes, leading to denial of service.
- Exploited in the wild
- Not known
- Login needed
- Any signed-in user
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2023-34462?
CVE-2023-34462 is a medium-severity denial of service vulnerability in Netty Netty, published on 22 Jun 2023. Any signed-in user can exploit it over the network, with no action from the victim.
Official description
Netty is an asynchronous event-driven network application framework for rapid development of maintainable high performance protocol servers & clients. 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. 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`. This vulnerability has been fixed in version 4.1.94.Final.
Which versions are affected by CVE-2023-34462?
2 open source packages ship an affected version, including io.netty:netty-handler. It affects 1 product.
| Package | Affected | Fixed in |
|---|---|---|
io.netty:netty-handler Maven | All versions | 4.1.94.Final |
io.netty:netty-handler Maven | All versions | 4.1.94.Final |
Linux distribution packages (8)
netty-tcnative SUSE:Linux Enterprise Module for Development Tools 15 SP4 | All versions | 2.0.61-150200.3.13.1 |
netty-tcnative SUSE:Linux Enterprise Module for Development Tools 15 SP5 | All versions | 2.0.61-150200.3.13.1 |
netty SUSE:Linux Enterprise Module for Package Hub 15 SP5 | All versions | 4.1.94-150200.4.17.1 |
netty-tcnative SUSE:Linux Enterprise Real Time 15 SP3 | All versions | 2.0.61-150200.3.13.1 |
netty openSUSE:Leap 15.4 | All versions | 4.1.94-150200.4.17.1 |
netty-tcnative openSUSE:Leap 15.4 | All versions | 2.0.61-150200.3.13.1 |
netty openSUSE:Leap 15.5 | All versions | 4.1.94-150200.4.17.1 |
netty-tcnative openSUSE:Leap 15.5 | All versions | 2.0.61-150200.3.13.1 |
Products include Netty Netty.
How do I fix CVE-2023-34462?
Upgrade io.netty:netty-handler to 4.1.94.Final or later.
Upgrade, then put limits on request size, rate and nesting depth so one client cannot exhaust the service. More about Denial of service.
Is CVE-2023-34462 being exploited?
There is no known exploitation of CVE-2023-34462 in the wild and no public exploit code.
Other vulnerabilities in Netty Netty
- CVE-2026-75595 Netty: SNI Routing Bypass via Fragmented TLS ClientHello Causing Fallback to Default SslContext
- CVE-2026-75596 Netty: Fragmented ClientHello records trigger quadratic pre-handshake reassembly in default SNI parsing
- CVE-2026-59901 Netty Bzip2Decoder: Infinite Loop in RLE State Machine Leads to Event-Loop Thread Hang
- CVE-2026-55851 Netty codec-haproxy: Signed-Byte Sentinel Collision in HAProxyMessageDecoder Leads to Unbounded Memory Exhaustion
- CVE-2026-56745 Netty SpdyHttpDecoder: ByteBuf Reference Leak on RST_STREAM Leads to Native Memory Exhaustion
Sources
Also known as CLEANSTART-2026-IQ25144, CLEANSTART-2026-JJ44639, CLEANSTART-2026-SO54386, CLSA-2026-1776818207, DEBIAN-CVE-2023-34462, ECHO-271e-3fbf-886d and 6 more.