Summary
Netty has a Vulnerable Default Configuration Which Leads to Denial of Service via Unbounded HTTP/3 Header Size
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.
Crafted input forces the application to consume excessive CPU, memory, or other resources, degrading or denying service. Typical impact: denial of service.
CVE-2026-44892 has a CVSS score of 7.5 (High). The vector is network-reachable, no privileges required, and no user interaction. A CVSS score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether this affects your application depends on whether the vulnerable code is present and reachable in your environment. A fixed version is available (4.2.15.Final); upgrading removes the vulnerable code path.
Affected versions
Security releases
Kodem intelligence
Severity tells you how bad this could be in the worst case. It does not tell you whether you are exposed. Exploitability and impact are functions of runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A vulnerable package can sit in your dependency tree and never run.
Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter. Kodem's runtime-powered SCA identifies whether this CVE is reachable in your applications.
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Frequently Asked Questions
- What is CVE-2026-44892? CVE-2026-44892 is a high-severity uncontrolled resource consumption vulnerability in io.netty:netty-codec-http3 (maven), affecting versions >= 4.2.0.Final, <= 4.2.14.Final. It is fixed in 4.2.15.Final. Crafted input forces the application to consume excessive CPU, memory, or other resources, degrading or denying service.
- How severe is CVE-2026-44892? CVE-2026-44892 has a CVSS score of 7.5 (High). This score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether it represents real risk in your environment depends on whether the vulnerable code is present and reachable.
- Which versions of io.netty:netty-codec-http3 are affected by CVE-2026-44892? io.netty:netty-codec-http3 (maven) versions >= 4.2.0.Final, <= 4.2.14.Final is affected.
- Is there a fix for CVE-2026-44892? Yes. CVE-2026-44892 is fixed in 4.2.15.Final. Upgrade to this version or later.
- Is CVE-2026-44892 exploitable, and should I be worried? Whether CVE-2026-44892 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
- What actually determines whether CVE-2026-44892 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
- How do I fix CVE-2026-44892? Upgrade
io.netty:netty-codec-http3to 4.2.15.Final or later.