Vulnerability 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.
CVSS Score
HIGH
Related Weaknesses (CWE)
References
- https://github.com/netty/netty/security/advisories/GHSA-v5p2-hmgx-3xrx
- https://www.vulncheck.com/advisories/netty-http-3-qpack-prefixed-integer-dos-via
FAQ
What is CVE-2026-100661?
CVE-2026-100661 is a vulnerability with a CVSS score of 7.5 (HIGH). 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.decodePrefixedInt...
How severe is CVE-2026-100661?
CVE-2026-100661 has been rated HIGH with a CVSS base score of 7.5/10. Review the CVSS metrics above for detailed severity breakdown.
Is there a patch for CVE-2026-100661?
Check the references section above for vendor advisories and patch information. Review vendor security bulletins for remediation guidance.