Resource exhaustion in Netty
CVE-2026-100661
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.
Vulnerability class: DoS (Denial of Service)
Published .
CVSS v3 metric
CVSS v3 base score 7.5 (High). Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H.
EPSS exploit prediction
No EPSS score from FIRST.org yet. New CVEs usually get one within a few days; no score means no signal yet, not low risk. How EPSS works.
Affected products
Weakness classification (CWE)
References
- github.com/netty/netty/security/advisories/GHSA-v5p2-hmgx-3xrx (vendor-advisory)
- www.vulncheck.com/advisories/netty-http-3-qpack-prefixed-integer-dos-via-unboun… (third-party-advisory)
Frequently asked questions
- What is CVE-2026-100661?
- CVE-2026-100661 is a high-severity vulnerability in Netty, classified under Uncontrolled Resource Consumption. CVSS score: 7.5/10. Published 2026-09-26.
- How severe is CVE-2026-100661?
- High severity. CVSS v3 base score is 7.5 out of 10.