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HIGH severity

CVE-2026-44892 — netty-codec-http3

HIGH

CVE-2026-44892 is a high-severity (CVSS 7.5) Uncontrolled Resource Consumption vulnerability in io.netty:netty-codec-http3. A fix is available for io.netty:netty-codec-http3 — see the affected versions and patch details below.

Netty has a Vulnerable Default Configuration Which Leads to Denial of Service via Unbounded HTTP/3 Header Size

Also known asGHSA-c2rx-5r8w-8xr2
Published
Jun 12, 2026
Updated
Aug 12, 2026
Affected
1 pkg
Patched
1 / 1
Exploits
None indexed
Exploitation data as of Sep 27, 2026 · OSV.dev, NVD, FIRST.org (EPSS)

Exploitation Status

No confirmed exploitation observed yet

  • CISA assesses this as automatable — exploitation doesn’t require manual, per-target effort, which raises the odds of mass scanning and opportunistic attacks.
  • CISA’s own triage has not observed active exploitation or public proof-of-concept code for this CVE as of its last assessment.

Exploitation and automatability from CISA’s SSVC triage for CVE-2026-44892.

EPSS Exploitation Probability

via FIRST.org ↗
0.5%probability of exploitation in next 30 days
Lower Risk0.00%
Lower risk than most CVEs40th percentile — riskier than 40% of all scored CVEsHighest risk

Probability of exploitation in the next 30 days, from FIRST.org EPSS.

How urgent is this, really

CVE-2026-44892 by exploitation likelihood (EPSS) against impact (CVSS). Outside the shaded patch-first corner.

Where this sits among everything scored

Of 379,842 CVEs with a current EPSS score, this one falls in the < 10% band (highlighted). Counts from FIRST.org, log-scaled.

Real-World Exposure

1 pkg affected
☕io.netty:netty-codec-http3

Real-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

Summary

The default configuration of the Http3ConnectionHandler in the Netty HTTP/3 codec lacks an enforced maximum header size limit. When a peer does not explicitly specify HTTP3_SETTINGS_MAX_FIELD_SECTION_SIZE, the implementation defaults to an unbounded limit. This insecure default configuration allows a malicious client or server to send an enormous number of headers, leading to a memory exhaustion Denial of Service via an OutOfMemoryError.

Details

Netty securely limits header sizes for older protocols. In HTTP/1.1, Netty strictly enforces an 8192-byte limit out-of-the-box via HttpObjectDecoder. For HTTP/2, while RFC 9113 specifies that SETTINGS_MAX_HEADER_LIST_SIZE defaults to unlimited, Netty securely overrides this RFC default by enforcing an 8192-byte limit (Http2CodecUtil.DEFAULT_HEADER_LIST_SIZE).

However, this secure-by-default configuration is missing in the HTTP/3 implementation. While Netty provides a mechanism to configure the maximum header field section size via Http3Settings, its out-of-the-box behaviour strictly follows RFC 9114's unlimited default.

Because many developers rely on the framework's default configurations and basic constructors, their applications are unknowingly left vulnerable. This nearly infinite default limit is passed into Http3FrameCodec#newFactory and stored as maxHeaderListSize inside Http3FrameCodec.

A bad actor can continuously send HTTP/3 headers within a connection, exploiting the insecure default configuration to consume server memory unconditionally until the application crashes with an OutOfMemoryError.

Impact

Denial of Service via memory exhaustion. All applications using Netty's HTTP/3 codec with its default configuration are impacted.

Affected Packages

1 total 1 fixed
EcosystemPackageVulnerable rangeFix
☕Mavenio.netty:netty-codec-http3≥ 4.2.0.Final&&< 4.2.15.Final4.2.15.Finalio.netty:netty-codec-http3:4.2.15.Final

Affected Products

1 product · 1 configurations
Application
nettynetty
≥ 4.2.0 && < 4.2.15
range

Detection & mitigation playbook

Open-source dependency

  1. Detect

    Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for io.netty:netty-codec-http3, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.

  2. Fix

    Update io.netty:netty-codec-http3 to 4.2.15.Final or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-44892 is resolved across your whole dependency graph.

  3. Workarounds

    Cap what an attacker can consume: apply request size, rate and timeout limits in front of the affected component, and run it with memory and CPU limits so exhaustion degrades one worker rather than the whole service.

Frequently Asked Questions

### Summary The default configuration of the `Http3ConnectionHandler` in the Netty HTTP/3 codec lacks an enforced maximum header size limit. When a peer does not explicitly specify `HTTP3_SETTINGS_MAX_FIELD_SECTION_SIZE`, the implementation defaults to an unbounded limit. This insecure default configuration allows a malicious client or server to send an enormous number of headers, leading to a memory exhaustion Denial of Service via an `OutOfMemoryError`. ### Details Netty securely limits header sizes for older protocols. In HTTP/1.1, Netty strictly enforces an `8192`-byte limit out-of-the-bo
O3 Security · Impact-Aware SCA

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CVE-2026-44892: netty-codec DoS (High 7.5) | O3 Security