CVE-2026-42587 — netty-codec-http
HIGHCVE-2026-42587 is a high-severity (CVSS 7.5) Uncontrolled Resource Consumption vulnerability in io.netty:netty-codec-http. A fix is available for io.netty:netty-codec-http — see the affected versions and patch details below.
Netty: HttpContentDecompressor maxAllocation bypass via Content-Encoding: br/zstd/snappy enables decompression bomb DoS
Exploitation Status
Proof-of-concept exploit code exists
- CISA’s SSVC triage found public proof-of-concept exploit code for this CVE, though no confirmed active exploitation.
- CISA assesses this as automatable — exploitation doesn’t require manual, per-target effort, which raises the odds of mass scanning and opportunistic attacks.
Exploitation and automatability from CISA’s SSVC triage for CVE-2026-42587.
EPSS Exploitation Probability
EPSS (Exploit Prediction Scoring System) is a daily probability model maintained by FIRST.org. It estimates the likelihood a CVE will be exploited in production environments within the next 30 days, derived from real-world threat intelligence signals.
How urgent is this, really
CVE-2026-42587 plotted by exploitation likelihood (EPSS) against impact (CVSS). The shaded corner — EPSS 50%+ and CVSS 7.0+ — is where this CVE doesn't sit, though severity or exploitability alone can still warrant action.
Where this sits among everything scored
Of 377,333 CVEs with a current EPSS score, this one falls in the < 10% band (highlighted). Real counts from FIRST.org, not a sample — log-scaled since the landscape is heavily right-skewed.
Real-World Exposure
io.netty:netty-codec-http☕io.netty:netty-codec-http2☕io.netty:netty-codec-http☕io.netty:netty-codec-http2Real-time download stats are indexed for npm and PyPI packages. This vulnerability affects Maven packages — download data is not available via public APIs for these ecosystems.
Description
Netty is an asynchronous, event-driven network application framework. Prior to 4.2.13.Final and 4.1.133.Final, HttpContentDecompressor accepts a maxAllocation parameter to limit decompression buffer size and prevent decompression bomb attacks. This limit is correctly enforced for gzip and deflate encodings via ZlibDecoder, but is silently ignored when the content encoding is br (Brotli), zstd, or snappy. An attacker can bypass the configured decompression limit by sending a compressed payload with Content-Encoding: br instead of Content-Encoding: gzip, causing unbounded memory allocation and out-of-memory denial of service. The same vulnerability exists in DelegatingDecompressorFrameListener for HTTP/2 connections. This vulnerability is fixed in 4.2.13.Final and 4.1.133.Final.
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| ☕Maven | io.netty:netty-codec-http | ≥ 4.2.0.Alpha1&&< 4.2.13.Final | 4.2.13.Finalio.netty:netty-codec-http:4.2.13.Final |
| ☕Maven | io.netty:netty-codec-http2 | ≥ 4.2.0.Alpha1&&< 4.2.13.Final | 4.2.13.Finalio.netty:netty-codec-http2:4.2.13.Final |
| ☕Maven | io.netty:netty-codec-http | all versions | 4.1.133.Finalio.netty:netty-codec-http:4.1.133.Final |
| ☕Maven | io.netty:netty-codec-http2 | all versions | 4.1.133.Finalio.netty:netty-codec-http2:4.1.133.Final |
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for io.netty:netty-codec-http, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update io.netty:netty-codec-http to 4.2.13.Final or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-42587 is resolved across your whole dependency graph.
Workarounds
If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.
How O3 protects you
O3 Security's impact-aware SCA analyses which vulnerable code paths your application actually calls, so a match like CVE-2026-42587 can be triaged on real exposure rather than presence alone.
Tailored to CVE-2026-42587. Runtime protection reduces exposure until a permanent patch is applied and verified — it complements patching, it doesn't replace it.
Fixing This On Your OS
If you run this on a Linux distribution, patch through your package manager against the distro's own security advisory below — it tracks the exact backported fix for your release, which can ship on a different timeline (and sometimes a different severity) than the upstream project.
This is an Important denial of service vulnerability in Netty's HTTP content decompression. A remote attacker can exploit this flaw by sending specially crafted compressed payloads using Brotli, Zstandard, or Snappy encodings, bypassing configured decompression limits. This leads to unbounded memory allocation,…
| Product | Fixed in | Advisory |
|---|---|---|
| Cryostat 4 on RHEL 9 | cryostat/cryostat-reports-rhel9:4.2.0-10 | RHSA-2026:28010 |
| Red Hat AMQ Broker 7.13.6 | netty-codec-http | RHSA-2026:66545 |
| Red Hat AMQ Broker 7.14.1 | netty-codec-http | RHSA-2026:66488 |
| Red Hat build of Apache Camel 4.18.1.P1 for Spring Boot 3.5.16 | netty-codec-http | RHSA-2026:37390 |
| Red Hat build of Quarkus 3.27.4 | netty-codec-http | RHSA-2026:23808 |
| Red Hat build of Quarkus 3.33.2 | see advisory | RHSA-2026:24502 |
| Red Hat Data Grid 8.6.2 | netty-codec-http | RHSA-2026:41951 |
| Red Hat JBoss Enterprise Application Platform 7.4 ELS on RHEL 7 | eap7-activemq-artemis-0:2.16.0-22.redhat_00057.1.el7eap | RHSA-2026:53644 |
Frequently Asked Questions
Is CVE-2026-42587 in your dependencies?
O3 Security finds CVE-2026-42587 across Maven dependencies, including transitive ones, and its impact-aware SCA ranks findings by whether your code actually calls the vulnerable path.