CVE-2026-100661: netty Uncontrolled Resource Consumption

Vulnerability summary

CVE-2026-100661 is a high (CVSS 8.7) Uncontrolled Resource Consumption vulnerability in netty. EPSS estimates a 0.34% chance of exploitation in the next 30 days, higher than 26.5% of scored vulnerabilities.

Timeline

1. 26-09-2026
   PublishedVulnerability first disclosed.
2. 02-10-2026
   Last modifiedVulnerability information updated.

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.

• CWE-400Uncontrolled Resource ConsumptionThe product does not properly control the allocation and maintenance of a limited resource.