# Netty: HttpContentDecompressor maxAllocation bypass when Content-Encoding set to br/zstd/snappy leads to decompression bomb DoS

Advisory record · `GHSA-f6hv-jmp6-3vwv`

- **Identifiers:** `GHSA-f6hv-jmp6-3vwv` · `CVE-2026-42587`
- **State:** Confirmed
- **Severity:** CVSS 7.5 High
- **Critical:** No
- **Weakness (CWE):** [CWE-400](https://cwe.mitre.org/data/definitions/400.html) · [CWE-770](https://cwe.mitre.org/data/definitions/770.html)
- **Tags:** [Denial of service](https://agentprime.io/advisories/tag/dos.md)
- **Published:** 7 May 2026
- **Updated:** 10 Sept 2026
- **Reviewed by a person:** No

Published by the GitHub Advisory Database at 7 May 2026, 00:46 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.Alpha1, <4.2.13.Final || <4.1.133.Final`; fixed in `4.2.13.Final`, `4.1.133.Final`
- `io.netty:netty-codec-http2` (Maven): affected `>=4.2.0.Alpha1, <4.2.13.Final || <4.1.133.Final`; fixed in `4.2.13.Final`, `4.1.133.Final`

## Machine-written summary

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

> Netty's netty-codec-http (versions from 4.2.0.Alpha1 before 4.2.13.Final, and 4.1.x before 4.1.133.Final) and netty-codec-http2 (same affected ranges) ignore the maxAllocation limit when HttpContentDecompressor or DelegatingDecompressorFrameListener handles Content-Encoding br, zstd, or snappy. A remote client can send a decompression bomb with one of these encodings and cause unbounded memory allocation, leading to out-of-memory denial of service. Upgrade to netty-codec-http 4.2.13.Final or 4.1.133.Final, and netty-codec-http2 to the same versions.

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

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

- **CISA KEV:** Not listed.
- **EPSS:** 0.0099, the 62nd percentile, on 10 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-f6hv-jmp6-3vwv)

## Sources

- [GitHub Advisory Database: GHSA-f6hv-jmp6-3vwv](https://github.com/advisories/GHSA-f6hv-jmp6-3vwv)
- [OSV: GHSA-f6hv-jmp6-3vwv](https://osv.dev/vulnerability/GHSA-f6hv-jmp6-3vwv)
- <https://github.com/netty/netty/security/advisories/GHSA-f6hv-jmp6-3vwv>
- <https://nvd.nist.gov/vuln/detail/CVE-2026-42587>
- <https://github.com/netty/netty>

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-f6hv-jmp6-3vwv>, 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-f6hv-jmp6-3vwv/>. Everything for agents: <https://agentprime.io/llms.txt>.