# Netty: WebSockets V07/V08 handshaker missing Connection/Upgrade validation

Advisory record · `GHSA-4mp9-239f-g9hg`

- **Identifiers:** `GHSA-4mp9-239f-g9hg` · `CVE-2026-59898`
- **State:** Confirmed
- **Severity:** CVSS 6.3 Medium
- **Critical:** No
- **Weakness (CWE):** [CWE-444](https://cwe.mitre.org/data/definitions/444.html)
- **Tags:** [HTTP request smuggling](https://agentprime.io/advisories/tag/request-smuggling.md)
- **Published:** 22 Jul 2026
- **Updated:** 10 Sept 2026
- **Reviewed by a person:** No

Published by the GitHub Advisory Database at 22 Jul 2026, 21:48 UTC. agentprime has not analysed this yet, so whether it affects any app is not known.

## Affected packages

- `io.netty:netty-codec-http` (Maven): affected `>=4.2.0.Final, <4.2.16.Final || <4.1.136.Final`; fixed in `4.2.16.Final`, `4.1.136.Final`

## Machine-written summary

Summary written by Claude Haiku from the source advisory. Not reviewed by a person.

> Netty's netty-codec-http package, versions 4.2.0.Final before 4.2.16.Final and before 4.1.136.Final, has a WebSocket V07/V08 handshaker that skips checking the Connection and Upgrade headers. A remote attacker can send a request with a WebSocket version header and no upgrade headers, which can complete a protocol switch that a proxy does not treat as an upgrade, enabling HTTP request smuggling and protocol-confusion attacks. Upgrade to netty-codec-http 4.2.16.Final or 4.1.136.Final.

Written 2 Nov 2026.

## Not analysed yet

We haven’t published our analysis of this Advisory yet. Once a person has reviewed it, this page will say what’s vulnerable, what has to be true for your app to be affected, and how to check.

## Severity and exploitation

- 6.3 Medium, CVSS 4.0: `CVSS:4.0/AV:N/AC:H/AT:N/PR:N/UI:N/VC:N/VI:N/VA:N/SC:L/SI:L/SA:N`, from CNA (GitHub_M)

- **CISA KEV:** Not listed.
- **EPSS:** 0.0044, the 38th percentile, on 5 Nov 2026: FIRST’s estimate of the chance of exploitation in the next 30 days.

## Timeline

- 31 Oct 2026, 14:16 UTC: First seen by agentprime
- 31 Oct 2026, 14:16 UTC: [Confirmed by OSV](https://osv.dev/vulnerability/GHSA-4mp9-239f-g9hg)

## Sources

- [GitHub Advisory Database: GHSA-4mp9-239f-g9hg](https://github.com/advisories/GHSA-4mp9-239f-g9hg)
- [OSV: GHSA-4mp9-239f-g9hg](https://osv.dev/vulnerability/GHSA-4mp9-239f-g9hg)
- <https://github.com/netty/netty/security/advisories/GHSA-4mp9-239f-g9hg>
- <https://github.com/netty/netty>
- <https://github.com/netty/netty/releases/tag/netty-4.1.136.Final>
- <https://github.com/netty/netty/releases/tag/netty-4.2.16.Final>

Facts on this page come from the GitHub Advisory Database (CC-BY 4.0), OSV and the other sources listed, as published. We don’t reproduce full advisory descriptions, which can contain exploit code.

## Check whether this affects you

A Match means an installed version is in the affected range above. Most don’t affect the app; agentprime hasn’t analysed this one yet.

- With the agentprime MCP server (<https://api.agentprime.io/mcp>), ask your agent to check the project: `check_lockfile` sends a lockfile, `check_packages` a list of installed packages, and both return the Matches and the upgrades that clear them. `get_advisory` returns this record. Setup: <https://agentprime.io/mcp.md>
- In a browser: <https://agentprime.io/check/> reads your lockfile in the browser, never uploading it.
- Whether it touches your code, with file and line: the Claude Code plugin, <https://agentprime.io/plugin.md>
- As JSON: <https://api.agentprime.io/v1/advisories/GHSA-4mp9-239f-g9hg>, or `POST https://api.agentprime.io/v1/match` with your packages (<https://agentprime.io/api.md>)

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The web page: <https://agentprime.io/advisories/GHSA-4mp9-239f-g9hg/>. Everything for agents: <https://agentprime.io/llms.txt>.