CVE-2026-55831: Netty SPDY SETTINGS frame overflows and crashes the server

Summary

A vulnerability in Netty's SPDY protocol implementation can cause a server to run out of memory or slow down when receiving a large SETTINGS frame from a remote peer. This can happen if the server is running an outdated version of Netty. To fix this, update to version 4.1.136.Final or 4.2.16.Final.

What to do

No fix is available yet. Check with your software vendor for updates.

Affected software

Vendor	Product	Affected versions
netty	netty	>= 4.2.0.Final, < 4.2.16.Final

Original title

Netty is a network application framework for development of protocol servers and clients. Prior to 4.1.136.Final and 4.2.16.Final, Netty's SPDY SETTINGS decoder accepts a peer-declared SETTINGS ent...

Original description

Netty is a network application framework for development of protocol servers and clients. Prior to 4.1.136.Final and 4.2.16.Final, Netty's SPDY SETTINGS decoder accepts a peer-declared SETTINGS entry count up to the 24-bit frame-length limit and materializes every unique setting ID in `DefaultSpdySettingsFrame`, allowing a remote SPDY/3.1 peer to send a syntactically valid roughly 2 MiB SETTINGS frame that creates 262144 map entries and amplifies network input into heap growth and ordered-map insertion work. This issue is fixed in versions 4.1.136.Final and 4.2.16.Final.

mitre CVSS3.1 7.5

Vulnerability type

CWE-770 Allocation of Resources Without Limits

CWE-400 Uncontrolled Resource Consumption

https://github.com/netty/netty/security/advisories/GHSA-6jqx-86gh-f27w x_refsource_CONFIRM
https://github.com/netty/netty/commit/5b68c61f37aa4a3045cba624cbea239655c9003b x_refsource_MISC
https://github.com/netty/netty/commit/bb2ff68a1fb71cb4b0eb9a9e17b66c52aff680c6 x_refsource_MISC
https://github.com/netty/netty/releases/tag/netty-4.1.136.Final x_refsource_MISC
https://github.com/netty/netty/releases/tag/netty-4.2.16.Final x_refsource_MISC