# 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. - **Severity:** Medium 6.5 (`CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H`) - **Exploited in the wild:** Not known - **Login needed:** Any signed-in user - **Attackable:** Over the internet - **Victim action needed:** Not needed - **Fix available:** Yes - **Published:** 22 Jun 2023 - **Updated:** 13 Feb 2025 - **Also known as:** CLEANSTART-2026-IQ25144, CLEANSTART-2026-JJ44639, CLEANSTART-2026-SO54386, CLSA-2026-1776818207, DEBIAN-CVE-2023-34462, ECHO-271e-3fbf-886d, GHSA-6mjq-h674-j845, MINI-c427-29rw-3hmj, MINI-fjr5-4gwv-qqhw, MINI-v3g6-99q9-f459, SUSE-SU-2023:2974-1, UBUNTU-CVE-2023-34462 ## 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. Weakness: CWE-770 (Allocation of Resources Without Limits or Throttling), CWE-400 (Uncontrolled Resource Consumption) ## 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 | Ecosystem | 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 | | `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: Netty Netty. ## How do I fix CVE-2023-34462? Upgrade io.netty:netty-handler to 4.1.94.Final or later. ## 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](https://insights.sbomify.com/CVE-2026-75595/): Netty: SNI Routing Bypass via Fragmented TLS ClientHello Causing Fallback to Default SslContext (critical 9.1) - [CVE-2026-75596](https://insights.sbomify.com/CVE-2026-75596/): Netty: Fragmented ClientHello records trigger quadratic pre-handshake reassembly in default SNI parsing (high 8.7) - [CVE-2026-59901](https://insights.sbomify.com/CVE-2026-59901/): Netty Bzip2Decoder: Infinite Loop in RLE State Machine Leads to Event-Loop Thread Hang (high 8.7) - [CVE-2026-55851](https://insights.sbomify.com/CVE-2026-55851/): Netty codec-haproxy: Signed-Byte Sentinel Collision in HAProxyMessageDecoder Leads to Unbounded Memory Exhaustion (high 8.7) - [CVE-2026-56745](https://insights.sbomify.com/CVE-2026-56745/): Netty SpdyHttpDecoder: ByteBuf Reference Leak on RST_STREAM Leads to Native Memory Exhaustion (high 8.7) ## Fix prompt for AI coding agents ```text Check this codebase for CVE-2023-34462 and fix it if it is affected. What it is: 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. Exploitation: There is no known exploitation of CVE-2023-34462 in the wild and no public exploit code. Affected packages and fixed versions: - io.netty:netty-handler (Maven): affected all versions; fixed in 4.1.94.Final - io.netty:netty-handler (Maven): affected all versions; fixed in 4.1.94.Final Task: 1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies. 2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it. 3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead. 4. Run the tests and summarise what changed and why. 5. If nothing in the project is affected, say so and change nothing. Reference: https://insights.sbomify.com/CVE-2023-34462/ (Markdown: https://insights.sbomify.com/CVE-2023-34462/index.md) ``` ## Sources - CVE record: https://www.cve.org/CVERecord?id=CVE-2023-34462 - NVD: https://nvd.nist.gov/vuln/detail/CVE-2023-34462 - OSV: https://osv.dev/vulnerability/CVE-2023-34462 --- From sbomify Insights: https://insights.sbomify.com/CVE-2023-34462/ Summaries are generated and may contain mistakes; the official description above is the record.