netty-handler SniHandler 16MB allocation

Exploitation

No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.

CVSS

6.5 · CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H

EPSS

• CVE-2023-34462: 2.46% estimated exploitation activity in the next 30 days; percentile 84.46 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.

As published by the source; long descriptions are shortened.

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…

Published by the source

20 Jun 2023, 16:33 UTC

Last modified by the source

24 Jun 2024, 21:24 UTC

Source last checked

26 Oct 2026, 16:30 UTC

1. Revision 1 · created · 26 Oct 2026

   Published from ghsa record GHSA-6mjq-h674-j845

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# Patch Next advisory brief: CVE-2023-34462

Advisory: netty-handler SniHandler 16MB allocation
IDs: CVE-2023-34462, GHSA-6mjq-h674-j845
Record: https://patchnext.com/advisories/cve-2023-34462 (revision 1, source checked 26 Oct 2026, 16:30 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: Medium (CVSS 6.5)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: io.netty:netty-handler 4.1.94.Final. A vendor fix does not mean a deployment is fixed.

## Affected components
- Maven io.netty:netty-handler: affected < 4.1.94.Final; fixed in 4.1.94.Final

## Suggested inspection (read-only)
- Maven io.netty:netty-handler: check the installed version with your package manager.

## Supported action
Upgrade each affected component to a fixed version on its release line. For a transitive dependency, upgrade the parent package or add an override or constraint, then regenerate the lockfile. Redeploy every environment that ran an affected version.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on io.netty:netty-handler.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://github.com/advisories/GHSA-6mjq-h674-j845 (GitHub-reviewed advisory GHSA-6mjq-h674-j845 lists affected ranges: Maven io.netty:netty-handler >=0 <4.1.94.Final)

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