rootpwn

high · CVSS v3 7.5 · CVSS v4 8.7

CVE-2026-100662

Netty's HTTP/3 codec allows an attacker to trigger unbounded heap growth via oversized QPACK literals, leading to denial of service. The fla

Overview

Netty's HTTP/3 codec allows an attacker to trigger unbounded heap growth via oversized QPACK literals, leading to denial of service. The flaw exists in versions 4.2.0.Final through 4.2.17.Final and is fixed in 4.2.18.Final.

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.

Impact

The vulnerability causes unbounded per‑connection heap allocation, resulting in OutOfMemoryError and service disruption. Availability is compromised for any server accepting HTTP/3 connections. Confidentiality and integrity remain unaffected.

Remediation

Upgrade Netty to 4.2.18.Final or later. If upgrade is not possible, disable HTTP/3 or enforce strict header size limits on the server. Monitor memory usage and apply rate limiting to mitigate potential DoS.

Risk context

Severity is high with CVSS v3 score 7.5 and v4 score 8.7. Although EPSS is not available, the lack of per‑instruction caps makes this a serious DoS risk for exposed HTTP/3 services.

Affected products

  • Netty 4.2.x HTTP/3 codec
  • Netty 4.2.x server
  • Netty 4.2.x client
  • Netty 4.2.x HTTP/3 library

Scores

Severity
high
CVSS v2
7.8
CVSS v3
7.5
CVSS v4
8.7
EPSS
—

netty http3 denial-of-service resource-exhaustion heap-oom qpack cve-2026-100662

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