Vulnerability · Published Jun 12, 2026 · Assigned by GitHub_M

CVE-2026-50020Netty's HttpObjectDecoder skips arbitrary initial control characters when only initial CRLF characters are permitted

Medium 5.3

In plain English

A medium-severity security flaw in netty from netty. Proof-of-concept exploit code is public. The chance it is exploited in the next 30 days is estimated at 0.2% (higher than 14% of all known vulnerabilities). Fixed versions are available - upgrade the affected package.

Severity (CVSS 3.1)5.3Medium

Exploit odds (30 days)0.2%top 85.8% of all CVEs

Exploited in the wildNo reportsCISA SSVC: poc

Attack toolingNoneno public tooling known

Official description

Netty is a network application framework for development of protocol servers and clients. Prior to versions 4.1.135.Final and 4.2.15.Final, before reading the first request-line, `HttpObjectDecoder` skips every byte for which `Character.isISOControl(b)` is `true` (0x00–0x1F and 0x7F) as well as all whitespace. RFC 9112 §2.2 only asks servers to ignore empty CRLF lines preceding the request-line — a carefully scoped robustness allowance intended to handle HTTP/1.0 POST workarounds. Silently absorbing NUL bytes, SOH, STX, and other non-CRLF control characters goes significantly beyond this, and can be exploited for request-boundary confusion in pipelined or multiplexed transports where a front-end component treats those bytes differently. Versions 4.1.135.Final and 4.2.15.Final patch the issue.

Affected packages & fixed versions

Ecosystem	Package	Fixed in	Advisory
Debian:12	netty	no fix listed	DEBIAN-CVE-2026-50020
Debian:13	netty	no fix listed	DEBIAN-CVE-2026-50020
Debian:14	netty	no fix listed	DEBIAN-CVE-2026-50020
Maven	io.netty:netty-codec-http	4.1.135.Final	GHSA-hvcg-qmg6-jm4c
Maven	io.netty:netty-codec-http	4.2.15.Final	GHSA-hvcg-qmg6-jm4c
Ubuntu:25.10	netty	no fix listed	UBUNTU-CVE-2026-50020
Ubuntu:26.10	netty	no fix listed	UBUNTU-CVE-2026-50020

Affected products (as reported)

Vendor	Product	Versions
netty	netty	>= 4.2.0.Final, < 4.2.15.Final< 4.1.135.Final

Weakness: CWE-444 · Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N

References

https://github.com/netty/netty/security/advisories/GHSA-hvcg-qmg6-jm4c x_refsource_CONFIRM
https://github.com/netty/netty/releases/tag/netty-4.1.135.Final x_refsource_MISC
https://github.com/netty/netty/releases/tag/netty-4.2.15.Final x_refsource_MISC