CVE-2026-100662
Received Received - Intake

Denial of Service in Netty HTTP/3 Codec via QPACK Encoder

Publication date: 2026-09-26

Last updated on: 2026-09-26

Assigner: VulnCheck

Description
Netty's HTTP/3 codec (io.netty:netty-codec-http3) versions 4.2.0.Final through 4.2.17.Final contain an uncontrolled resource consumption vulnerability in the QPACK encoder-stream instruction decoder (QpackEncoderHandler, installed on the peer-initiated unidirectional QPACK encoder stream, type 0x02). The handler accepts an attacker-declared string-literal length of up to Integer.MAX_VALUE (~2 GiB) for the Name Length and Value Length fields of the "Insert With Literal Name" instruction (RFC 9204 §4.3.3), with no per-instruction or per-literal length cap and no cumulation-size limit; the existing HTTP/3 limits (maxHeaderListSize, maxUnknownFramePayloadLength, DEFAULT_MAX_FIELD_SECTION_SIZE) are not applied to this handler. A remote, unauthenticated peer with an established HTTP/3 connection to a default Netty HTTP/3 server can declare a very large literal length and then trickle fewer bytes than declared, causing the ByteToMessageDecoder MERGE cumulator to retain and grow the per-connection buffer, and ultimately triggering a large byte-array allocation. This leads to unbounded per-connection heap growth and OutOfMemoryError, resulting in denial of service. Fixed in 4.2.18.Final.

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Meta Information

Published
2026-09-26
Last Modified
2026-09-26
Generated
2026-09-26
AI Q&A
2026-09-26
EPSS Evaluated
N/A
NVD
CVE-2026-100662
EUVD
EUVD-2026-87756

Affected Vendors & Products

Showing 4 associated CPEs
Vendor Product Version / Range
netty netty-codec-http3 From 4.2.0.Final (inc) to 4.2.17.Final (inc)
netty netty-codec-http3 4.2.18.Final
netty netty_codec_http3 From 4.2.0.Final (inc) to 4.2.17.Final (inc)
netty netty_codec_http3 4.2.18.Final

Helpful Resources

Exploitability

CWE
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KEV
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CWE ID Description
CWE-400 The product does not properly control the allocation and maintenance of a limited resource.

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Executive Summary

This vulnerability affects Netty's HTTP/3 codec versions 4.2.0.Final through 4.2.17.Final. It involves an uncontrolled resource consumption issue in the QPACK encoder-stream instruction decoder. An unauthenticated remote peer can exploit it by declaring an extremely large string-literal length (up to 2 GiB) for the 'Insert With Literal Name' instruction. This causes the decoder to retain and grow its buffer, leading to unbounded heap growth and eventually an OutOfMemoryError, resulting in denial of service.

Detection Guidance

Detecting this vulnerability requires checking the version of Netty's HTTP/3 codec (io.netty:netty-codec-http3) in use. If your system runs versions 4.2.0.Final through 4.2.17.Final, it is vulnerable. Use commands like 'mvn dependency:tree' for Maven or 'gradle dependencies' for Gradle to inspect dependencies.

Impact Analysis

This vulnerability allows a remote attacker to cause a denial of service by exhausting server memory. It can lead to service unavailability, crashes, or slowdowns for systems using vulnerable Netty HTTP/3 versions. The impact is severe as it requires no authentication or user interaction.

Mitigation Strategies

Upgrade Netty's HTTP/3 codec to version 4.2.18.Final or later immediately. This version includes fixes for the uncontrolled resource consumption vulnerability. If upgrading is not immediately possible, consider disabling HTTP/3 support or applying network-level mitigations to block malicious traffic.

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