CVE-2026-55831 netty CVE debrief

Who should care

Users of Netty versions prior to 4.1.136.Final and 4.2.16.Final should be aware of this vulnerability and take steps to mitigate it. This includes operators, platform administrators, vulnerability management teams, and security teams who may be impacted by the potential DoS attack.

Technical summary

The Netty 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`. This allows 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. The issue is fixed in versions 4.1.136.Final and 4.2.16.Final.

Defensive priority

High

Recommended defensive actions

• Update Netty to version 4.1.136.Final or 4.2.16.Final
• Implement traffic filtering to prevent malicious SETTINGS frames
• Monitor Netty applications for unusual traffic patterns
• Review compensating controls for exposed systems while remediation is scheduled and verified
• Check relevant monitoring, detection, and logs for exposed assets that need extra review
• Track exceptions, retest remediated assets, and close the item only after evidence is documented
• Confirm whether affected product deployments exist in managed environments and assign an owner for follow-up

Evidence notes

The CVE record was published on 2026-07-21T00:17:35.383Z and has been modified since then. The NVD entry is currently Analyzed. Evidence limits suggest that further review may be required to confirm affected scope and severity. Defenders should verify vendor guidance and assess potential impact on managed environments.

Official resources