CVE-2026-50560 — Netty susceptible to HTTP/2 Reset Attack with different on-the-wire signature

2026-09-30T21:46:01.862814+00:00

Affected: netty

Netty is a network application framework for development of protocol servers and clients. Prior to versions 4.1.135.Final and 4.2.15.Final, Netty HTTP/2 max header size handling produces an attack similar to HTTP/2 Rapid Reset. There is a setting in the http2 specification called `SETTINGS_MAX_HEADER_LIST_SIZE`. When a client sends that setting to Netty, it appears that Netty will behave as follows: read the request; proxy the request to the origin; attempt to produce a response; and create an exception while writing the headers for the response. Functionally, this should be similar to the http2 reset attack, but with a different on-the-wire signature. Versions 4.1.135.Final and 4.2.15.Final patch the issue.

GHSA-563q-j3cm-6jxm — Netty susceptible to HTTP/2 Reset Attack with different on-the-wire signature

2026-09-30T21:46:01.862919+00:00

Affected: Maven: io.netty:netty-codec-http2

### Summary

Netty HTTP/2 max header size handling produces attack similar to HTTP/2 Rapid Reset.

### Details

There is a setting in the http2 specification called `SETTINGS_MAX_HEADER_LIST_SIZE`. According to[ the RFC](https://www.rfc-editor.org/rfc/rfc9113.html#name-defined-settings): “This advisory setting informs a peer of the maximum field section size that the sender is prepared to accept, in units of octets.”

When a client sends that setting to Netty, it appears that Netty will behave as follows:

- Read the request - Proxy the request to the origin - Attempt to produce a response - Create an exception while writing the headers for the response

Functionally, this should be similar to the http2 reset attack, but with a different on-the-wire signature.

## Remediation

When speaking with clients, Netty should potentially treat this as “advisory” and ignore it. It would be best to ignore the SETTINGS_MAX_HEADER_LIST_SIZE setting from clients (or ignore it when sending to clients). According to the spec, a server does not need to honor this advisory setting, and it appears that other http/2 implementations ignore it when acting as a server.

### Impact

This is a DDoS attack similar to the HTTP/2 Rapid Reset Attack.

## Credit Jonathan Looney (Engineering, Netflix)

## Contact Ashley Tolbert (Security, Netflix) - artolbert@netflix.com

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CVE-2026-50560 — Netty susceptible to HTTP/2 Reset Attack with different on-the-wire signature

GHSA-563q-j3cm-6jxm — Netty susceptible to HTTP/2 Reset Attack with different on-the-wire signature