CVE-2026-55831: Netty SPDY SETTINGS frame count materializes unbounded settings map

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.

CVSS vector

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

Attack vector

Network

Complexity

Low

Privileges

None

User interaction

None

Confidentiality

None

Integrity

None

Availability

High

Scope

Unchanged

Exploitation

Is it being used?

Exploit prediction (EPSS)0.7% · higher than 52% of CVEs

Exploited in the wildNo evidence yet

CISA KEVNot listed

Ransomware campaign useNot known

Affected products

Which versions

NE

netty · netty

>= 4.2.0.Final, < 4.2.16.Final; >= 4.1.0.Final, < 4.1.136.Final · source: vendor, NVD