Netty HTTP/3 QPACK Prefixed Integer DoS via Unbounded Accumulation (CVE-2026-100661) | HOL Guard CVE

High · CVSS 8.7CVE-2026-100661

Netty HTTP/3 QPACK Prefixed Integer DoS via Unbounded Accumulation

Answer in brief

CVE-2026-100661 records a High severity (CVSS 8.7) vulnerability in Netty HTTP/3 QPACK Prefixed Integer DoS via Unbounded Accumulation. The current sources do not mark it as known exploited. The current feed maps netty/netty (generic). Check affected ranges and fixed versions before updating.

Analysis pending evidence review

HOL Guard separates source facts from reviewed analysis. See the methodology.

Published Sep 26, 2026Updated Sep 26, 2026Source checked Sep 26, 2026First seen by HOL Sep 26, 2026Material review Sep 26, 2026

Upstream Advisory

Key facts

Risk: High · CVSS 8.7
Exploitation: Not marked as known exploited
Affected software: 1 mapped package or product
Fix availability: Available

Why this deserves its current priority

CVSS is 8.7. The current sources do not mark it as known exploited. Treat this as a source-backed prioritization signal, not a statement about your environment.

Analysis status

Analysis pending evidence review

Factual feed record only; HOL analysis is not approved for indexing. Read the methodology.

Affected scope and exposure questions

The current feed maps netty/netty (generic). Check affected ranges and fixed versions before updating.

Mapped affected packages and fixed versions
Package	Affected range	Fixed version
netty/nettygeneric	>=4.2.0.Final <4.2.18.Final	4.2.18.Final

Recommended response

Check inventory. Check lockfiles and deployed manifests for netty/netty.
Review the reported fix. Update netty/netty to 4.2.18.Final if you use the affected versions. Test the change in a non-production environment first.

Evidence timeline and material changes

Published upstream
Sep 26, 2026
Evidence: source:cvelist:source_dates:source-dates:record
Source modified
Sep 26, 2026
Evidence: source:cvelist:source_dates:source-dates:record
First seen by HOL
Sep 26, 2026

Sources and claim methodology

Upstream source description

Netty's HTTP/3 codec (io.netty:netty-codec-http3) versions 4.2.0.Final through 4.2.17.Final contain a denial-of-service vulnerability in the QPACK prefixed-integer decoder (QpackUtil.decodePrefixedInteger), which does not bound the number of continuation bytes it will process. A remote, unauthenticated peer can open a QPACK unidirectional stream (type 0x02 encoder or 0x03 decoder) and send a first byte with all prefix bits set (e.g. 0xFF for a 7-bit prefix or 0x3F for a 5-bit prefix) followed by an endless run of 0x80 continuation bytes. The decoder returns -1 ('need more bytes'), so callers never consume the input, the ByteToMessageDecoder cumulator grows without bound, and each decode() invocation re-scans the whole accumulated buffer, yielding O(N^2) CPU cost. The result is unbounded per-connection heap growth (OutOfMemoryError) and event-loop CPU starvation, reachable in every configuration. Fixed in 4.2.18.Final.

Quoted source text, attributed separately from HOL analysis.