CVE-2026-55833

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.

Affected

netty

CVSS v3.1 GITHUB

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

EPSS

0.66% chance of exploitation in the next 30 days, 51st percentile

Published

2026-07-20

Updated

2026-07-21

Proof-of-concept exploits (1)

• advisories/GHSA-mvh2-crg5-v77c

Security advisories

• netty/netty/security/advisories/GHSA-mvh2-crg5-v77c
• netty/netty/commit/5b68c61f37aa4a3045cba624cbea239655c9003b

References

• CVE Record
• NVD entry