Netty SPDY Header Decompression CPU Amplification (4.1.135, <4.2.15)
CVE-2026-55833 Published on July 20, 2026
Netty SPDY zlib header block continues decoded expansion after maxHeaderSize truncation
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.
Vulnerability Analysis
CVE-2026-55833 can be exploited with network access, and does not require authorization privileges or user interaction. This vulnerability is considered to have a low attack complexity. The potential impact of an exploit of this vulnerability is considered to have no impact on confidentiality and integrity, and a high impact on availability.
Weakness Type
What is a Resource Exhaustion Vulnerability?
The software does not properly control the allocation and maintenance of a limited resource, thereby enabling an actor to influence the amount of resources consumed, eventually leading to the exhaustion of available resources.
CVE-2026-55833 has been classified to as a Resource Exhaustion vulnerability or weakness.
Products Associated with CVE-2026-55833
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Affected Versions
netty:- Version >= 4.2.0.Final, < 4.2.16.Final is affected.
- Version >= 4.1.0.Final, < 4.1.136.Final is affected.
Exploit Probability
EPSS (Exploit Prediction Scoring System) scores estimate the probability that a vulnerability will be exploited in the wild within the next 30 days. The percentile shows you how this score compares to all other vulnerabilities.