# CVE-2026-42587: Netty denial of service via decompression limit bypass

Source: https://junglewise.ai/threats/cve-2026-42587-netty-denial-of-service-via-decompression-limit-bypass  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-05-13. Updated: 2026-05-18  
License: CC BY 4.0 with a link back

CVE-2026-42587 · Severity: high · CVSS 7.5 · Published 2026-05-13

Netty is a widely used networking framework that helps Java applications handle web traffic. A security flaw allows attackers to bypass built-in protections designed to prevent 'decompression bombs'—maliciously crafted files that expand to a massive size when opened. By sending these files using specific compression formats like Brotli or Zstd, an attacker can crash the server by exhausting its memory, leading to a total service outage.

Technologies: [io.netty:netty-codec-http (Maven)](https://junglewise.ai/threats/technologies/io-netty-netty-codec-http), [io.netty:netty-codec-http2 (Maven)](https://junglewise.ai/threats/technologies/io-netty-netty-codec-http2), [Netty Project Codec HTTP](https://junglewise.ai/threats/technologies/codec-http). Vendors: [Maven](https://junglewise.ai/threats/vendors/maven), [Netty Project](https://junglewise.ai/threats/vendors/netty-project).

## Quick answers

**Is CVE-2026-42587 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-42587 being exploited in the wild.

**How severe is CVE-2026-42587?** High severity, with a CVSS score of 7.5, published 13 May 2026.

**Which products and versions are affected?** io.netty:netty-codec-http (Maven) ECOSYSTEM:introduced=4.2.0.Alpha1,fixed=4.2.13.Final; io.netty:netty-codec-http2 (Maven) ECOSYSTEM:introduced=4.2.0.Alpha1,fixed=4.2.13.Final.

**Is there a fix for CVE-2026-42587?** Yes. io.netty:netty-codec-http (Maven): upgrade to 4.2.13.Final or later; io.netty:netty-codec-http2 (Maven): upgrade to 4.2.13.Final or later. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

**How is CVE-2026-42587 attacked?** It is attacked over the network, in a software library.

**Am I affected by CVE-2026-42587?** Check whether you run io.netty:netty-codec-http (Maven), io.netty:netty-codec-http2 (Maven), Netty Project Codec HTTP or one of the others listed at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

## How to fix

- io.netty:netty-codec-http (Maven): upgrade to 4.2.13.Final or later

  ```sh
  # set io.netty:netty-codec-http to 4.2.13.Final in your pom.xml or build.gradle
  ```

- io.netty:netty-codec-http2 (Maven): upgrade to 4.2.13.Final or later

  ```sh
  # set io.netty:netty-codec-http2 to 4.2.13.Final in your pom.xml or build.gradle
  ```


## Technical details

A resource consumption vulnerability exists in Netty's HttpContentDecompressor and DelegatingDecompressorFrameListener. While the framework provides a 'maxAllocation' parameter to limit decompression buffer sizes, this limit is only enforced for gzip and deflate encodings. When an attacker specifies 'br' (Brotli), 'zstd', or 'snappy' in the Content-Encoding header, the limit is ignored, leading to unbounded memory allocation. This allows a remote, unauthenticated attacker to trigger an OutOfMemoryError (OOM) and crash the application by sending a small, highly compressed payload. The issue is resolved in versions 4.2.13.Final and 4.1.133.Final by properly passing and enforcing the allocation limits across all supported decoders.

## Affected products

- Netty netty-codec-http <= 4.2.12.Final, <= 4.1.132.Final
- Netty netty-codec-http2 <= 4.2.12.Final, <= 4.1.132.Final

## Identifiers

- CVE-2026-42587
- GHSA-f6hv-jmp6-3vwv

## Timeline

- 2026-05-05: advisory: GitHub Security Advisory published
- 2026-05-13: disclosed: CVE published to NVD

## References

- [https://github.com/netty/netty/security/advisories/GHSA-f6hv-jmp6-3vwv](https://github.com/netty/netty/security/advisories/GHSA-f6hv-jmp6-3vwv)

## Related threats

- [Netty CorsHandler cache poisoning via Vary header overwrite](https://junglewise.ai/threats/cve-2026-59903-netty-corshandler-cache-poisoning-via-vary-header-overwrite)
- [Netty HTTP request smuggling via lax WebSocket handshake validation](https://junglewise.ai/threats/cve-2026-59898-netty-http-request-smuggling-via-lax-websocket-handshake)
- [Netty request smuggling via Host header duplication in HTTP/2 translation](https://junglewise.ai/threats/cve-2026-59900-netty-request-smuggling-via-host-header-duplication-in-http-2)
- [Netty resource exhaustion in HttpContentEncoder via HTTP pipelining](https://junglewise.ai/threats/cve-2026-59899-netty-resource-exhaustion-in-httpcontentencoder-via-http)
- [Netty CRLF injection in HttpPostRequestEncoder multipart filenames](https://junglewise.ai/threats/cve-2026-59921-netty-crlf-injection-in-httppostrequestencoder-multipart)