# Possible request smuggling in HTTP/2 due missing validation

Advisory record · `GHSA-wm47-8v5p-wjpj`

- **Identifiers:** `GHSA-wm47-8v5p-wjpj` · `BIT-zookeeper-2021-21295` · `CVE-2021-21295`
- **State:** Confirmed
- **Severity:** CVSS 5.9 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:** 9 Mar 2021
- **Updated:** 10 Sept 2026
- **Reviewed by a person:** No

Published by the GitHub Advisory Database at 9 Mar 2021, 18:49 UTC. agentprime has not analysed this yet, so whether it affects any app is not known.

## Affected packages

- `io.netty:netty-codec-http2` (Maven): affected `>=4.0.0, <4.1.60.Final`; fixed in `4.1.60.Final`
- `org.jboss.netty:netty` (Maven): affected `all versions`; no fixed version yet
- `io.netty:netty` (Maven): affected `all versions`; no fixed version yet

## Machine-written summary

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

> Netty's io.netty:netty-codec-http2 versions from 4.0.0 before 4.1.60.Final do not validate the Content-Length header on HTTP/2 requests. An attacker who can send HTTP/2 requests to a proxy that converts them to HTTP/1.1 and forwards them to a remote peer can smuggle requests inside the body. Upgrade to io.netty:netty-codec-http2 4.1.60.Final or later. Users can instead add a custom ChannelInboundHandler behind Http2StreamFrameToHttpObjectCodec that performs the Content-Length validation. No fixed version is listed for org.jboss.netty:netty or io.netty:netty.

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

- 5.9 Medium, CVSS 3.1: `CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:H/A:N`, from CNA (GitHub_M)

- **CISA KEV:** Not listed.
- **EPSS:** 0.19, the 97th percentile, on 8 Nov 2026: FIRST’s estimate of the chance of exploitation in the next 30 days.

## Timeline

- 31 Oct 2026, 14:18 UTC: First seen by agentprime
- 31 Oct 2026, 14:18 UTC: [Confirmed by OSV](https://osv.dev/vulnerability/GHSA-wm47-8v5p-wjpj)

## Sources

- [GitHub Advisory Database: GHSA-wm47-8v5p-wjpj](https://github.com/advisories/GHSA-wm47-8v5p-wjpj)
- [OSV: GHSA-wm47-8v5p-wjpj](https://osv.dev/vulnerability/GHSA-wm47-8v5p-wjpj)
- <https://github.com/netty/netty/security/advisories/GHSA-wm47-8v5p-wjpj>
- <https://nvd.nist.gov/vuln/detail/CVE-2021-21295>
- <https://github.com/Netflix/zuul/pull/980>
- <https://github.com/netty/netty/commit/89c241e3b1795ff257af4ad6eadc616cb2fb3dc4>
- <https://lists.apache.org/thread.html/rc73b8dd01b1be276d06bdf07883ecd93fe1a01f139a99ef30ba4308c@%3Ccommits.servicecomb.apache.org%3E>
- <https://lists.apache.org/thread.html/rc165e36ca7cb5417aec3f21bbc4ec00fb38ecebdd96a82cfab9bd56f@%3Cjira.kafka.apache.org%3E>
- <https://lists.apache.org/thread.html/rc0087125cb15b4b78e44000f841cd37fefedfda942fd7ddf3ad1b528@%3Cissues.zookeeper.apache.org%3E>
- <https://lists.apache.org/thread.html/rbed09768f496244a2e138dbbe6d2847ddf796c9c8ef9e50f2e3e30d9@%3Cnotifications.zookeeper.apache.org%3E>
- <https://lists.apache.org/thread.html/rbadcbcb50195f00bbd196403865ced521ca70787999583c07be38d0e@%3Cnotifications.zookeeper.apache.org%3E>
- <https://lists.apache.org/thread.html/rb95d42ce220ed4a4683aa17833b5006d657bc4254bc5cb03cd5e6bfb@%3Cissues.hbase.apache.org%3E>
- <https://lists.apache.org/thread.html/rb592033a2462548d061a83ac9449c5ff66098751748fcd1e2d008233@%3Cissues.zookeeper.apache.org%3E>
- <https://lists.apache.org/thread.html/rb523bb6c60196c5f58514b86a8585c2069a4852039b45de3818b29d2@%3Ccommits.servicecomb.apache.org%3E>

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-wm47-8v5p-wjpj>, 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-wm47-8v5p-wjpj/>. Everything for agents: <https://agentprime.io/llms.txt>.