Memory Exhaustion in Netty HTTP/3 via Unbounded Headers

Executive Summary

CVE-2026-44892 is a vulnerability in Netty's HTTP/3 codec, specifically in the Http3ConnectionHandler. The default configuration does not enforce a maximum header size limit when the peer does not specify the HTTP3_SETTINGS_MAX_FIELD_SECTION_SIZE setting. This results in an unbounded header size limit, allowing a malicious client or server to send an extremely large number of headers.

Because of this, the system can experience memory exhaustion, leading to a Denial of Service (DoS) caused by an OutOfMemoryError. This issue arises because, unlike HTTP/1.1 and HTTP/2 where secure header size limits are enforced by default, HTTP/3 relies on RFC 9114 which defines an unlimited default, making the default Netty configuration insecure.

The vulnerability is addressed in Netty version 4.2.15.Final by enforcing a secure maximum header size limit.

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Impact Analysis

This vulnerability can lead to a Denial of Service (DoS) attack against applications using Netty's HTTP/3 codec with default settings. An attacker can exploit the lack of a maximum header size limit to send an enormous number of headers, causing the application to consume excessive memory.

The resulting memory exhaustion triggers an OutOfMemoryError, which can crash the application or severely degrade its performance, making it unavailable to legitimate users.

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Mitigation Strategies

To mitigate this vulnerability, you should upgrade Netty to version 4.2.15.Final or later, which contains a patch that enforces a secure maximum header size limit in the Http3ConnectionHandler.

This update prevents malicious clients or servers from sending excessively large HTTP/3 headers that could cause memory exhaustion and denial of service.

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Compliance Impact

The vulnerability CVE-2026-44892 allows a malicious actor to cause a denial of service via memory exhaustion by sending excessively large HTTP/3 headers due to an insecure default configuration in Netty's HTTP/3 codec.

While the vulnerability leads to a high-severity denial of service condition, there is no direct information provided about its impact on compliance with common standards and regulations such as GDPR or HIPAA.

Denial of service attacks can indirectly affect compliance by causing service unavailability, which might impact regulatory requirements for availability and reliability, but no explicit linkage or assessment is given in the provided resources.

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