High 7.5Published Sep 26, 2026

CVE-2026-100661Netty HTTP/3 QPACK Prefixed Integer DoS via Unbounded Accumulation

Updated under an hour ago (2026-10-19 06:30 UTC)

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EPSS puts the chance of exploitation in the next 30 days at 0.34%, higher than 26% of scored CVEs.

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Exploited in the last 30 days

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.

CVSS: 7.5 HIGH (v3.1, CNA)CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
Weakness (CWE): CWE-400
Known exploited: Not in CISA's KEV catalog
EPSS (exploitation in the next 30 days): 0.34% (percentile 26)
Assigned by: VulnCheck
NVD analysis: Deferred
Record last updated: Oct 2, 2026
First seen by InfoSec Signals: Oct 9, 2026

Affected products

Affected products

netty netty netty:netty (from the name)	from 4.2.0.Final before 4.2.18.Final; 4.2.18.Final not affected	CNA record

References

https://github.com/netty/netty/security/advisories/GHSA-v5p2-hmgx-3xrxvendor-advisory
https://www.vulncheck.com/advisories/netty-http-3-qpack-prefixed-integer-dos-via-unbounded-accumulationthird-party-advisory

The CVE record on cve.org NVD's entry

The CVE record is authoritative. Products marked “from the name” were identified from the CNA's free-text names, not a CPE, and are matched less certainly. This product uses the NVD API but is not endorsed or certified by the NVD.