Vulnerability · Published Jul 20, 2026 · Assigned by GitHub_M

CVE-2026-55833Netty SPDY zlib header block continues decoded expansion after maxHeaderSize truncation

High 7.5

In plain English

A high-severity uncontrolled resource consumption in netty from netty. There are no confirmed reports of exploitation so far. The chance it is exploited in the next 30 days is estimated at 0.7% (higher than 52% of all known vulnerabilities). Fixed versions are available - upgrade the affected package.

Severity (CVSS 3.1)7.5High

Exploit odds (30 days)0.7%top 48.0% of all CVEs

Exploited in the wildNo reportsCISA SSVC: none

Attack toolingNoneno public tooling known

Official 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 SPDY header decoding continues inflating zlib-compressed header blocks after the raw header parser has exceeded `maxHeaderSize` and marked the frame truncated in `SpdyFrameCodec`, allowing a remote peer to send a small compressed `HEADERS` block that expands into much larger raw header data and causes compression-amplified CPU and allocation churn. This issue is fixed in versions 4.1.136.Final and 4.2.16.Final.

Affected packages & fixed versions

Ecosystem	Package	Fixed in	Advisory
Debian:12	netty	no fix listed	DEBIAN-CVE-2026-55833
Debian:13	netty	no fix listed	DEBIAN-CVE-2026-55833
Debian:14	netty	no fix listed	DEBIAN-CVE-2026-55833
Maven	io.netty:netty-codec-http	4.2.16.Final	GHSA-mvh2-crg5-v77c
Maven	io.netty:netty-codec-http	4.1.136.Final	GHSA-mvh2-crg5-v77c
Ubuntu:26.10	netty	no fix listed	UBUNTU-CVE-2026-55833

Affected products (as reported)

Vendor	Product	Versions
netty	netty	>= 4.2.0.Final, < 4.2.16.Final>= 4.1.0.Final, < 4.1.136.Final

Weakness: CWE-400 · Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

References

https://github.com/netty/netty/security/advisories/GHSA-mvh2-crg5-v77c 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