🛡️ CVE-2026-59900 — netty

🟡 CVSS 5.3 — Medium ✅ No Known Exploit CWE-444 NVD
5.3
CVSS Score
0 Low4 Medium7 High9 Critical10

Description

Netty is an asynchronous, event-driven network application framework. Prior to versions 4.1.136.Final and 4.2.16.Final, Netty's HTTP/2-to-HTTP/1.x translation layer (Http2StreamFrameToHttpObjectCodec and InboundHttp2ToHttpAdapter) fails to deduplicate or validate Host headers when an HTTP/2 client supplies both the :authority pseudo-header and a literal host header in a single HEADERS frame. The translator maps :authority to Host and separately copies the literal host header, producing an HttpRequest object containing two Host headers with attacker-controlled differing values. This issue has been fixed in versions 4.1.136.Final and 4.2.16.Final.

How this vulnerability can be exploited

This issue can be reached over the network, attack complexity is low, an attacker needs no privileges on the target. No user interaction is required. The scope is unchanged, so the impact stays within the vulnerable component. Rated impact: confidentiality none, integrity low, availability none.

Weakness class

CVE-2026-59900 is classified as CWE-444: HTTP Request Smuggling. A proxy and a server disagree on where one request ends, letting an attacker slip a second request past the front end.

Affected software

CVE-2026-59900 is recorded against 2 packages.

  • io.netty:netty-codec-http2 (fixed in 4.1.136.Final)
  • netty (from 4.2.0 up to 4.2.16)

Timeline and source

Published on 22 July 2026 and last revised on 24 July 2026. No public exploit is currently recorded for this entry. Record sourced from NVD.

References

github.com (Web)
github.com (Package)
github.com (Web)
github.com (Web)

Details

Severity Medium
CVSS Score 5.3
CVSS Vector CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N
CWE CWE-444
Public Exploit ✅ No
Source NVD
Published 2026-07-22
Updated 2026-08-12
Modified 2026-07-24
Fix URL N/A

Affected Packages

Software From version Fixed in
io.netty:netty-codec-http2 — 4.1.136.Final
netty 4.2.0 4.2.16

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