{"id":"CVE-2026-100661","summary":"Netty HTTP/3 QPACK Prefixed Integer DoS via Unbounded Accumulation","details":"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.","aliases":["GHSA-v5p2-hmgx-3xrx"],"modified":"2026-09-30T03:31:00.824183422Z","published":"2026-09-26T13:23:28.303Z","database_specific":{"cwe_ids":["CWE-400"],"osv_generated_from":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/100xxx/CVE-2026-100661.json","cna_assigner":"VulnCheck"},"references":[{"type":"ADVISORY","url":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/100xxx/CVE-2026-100661.json"},{"type":"ADVISORY","url":"https://github.com/netty/netty/security/advisories/GHSA-v5p2-hmgx-3xrx"},{"type":"ADVISORY","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-100661"},{"type":"ADVISORY","url":"https://www.vulncheck.com/advisories/netty-http-3-qpack-prefixed-integer-dos-via-unbounded-accumulation"}],"affected":[{"ranges":[{"type":"GIT","repo":"https://github.com/netty/netty","events":[{"introduced":"09e64d259c99be8b5b2a471a78f11e65eb82598a"},{"fixed":"2521f494432e27415a567d3a81a9eb907abf20b3"}],"database_specific":{"extracted_events":[{"introduced":"4.2.0.Final"},{"fixed":"4.2.18.Final"},{"fixed":"4.2.17.Final"}],"source":["AFFECTED_FIELD","DESCRIPTION"]}}],"versions":["netty-clang-bin","netty-4.2.17.Final","netty-4.2.16.Final","netty-4.2.15.Final","netty-4.2.14.Final","netty-4.2.13.Final","netty-4.2.12.Final","netty-4.2.11.Final","netty-4.2.10.Final","netty-4.2.9.Final","netty-4.2.8.Final","netty-4.2.7.Final","netty-4.2.6.Final","netty-4.2.5.Final","netty-4.2.4.Final","netty-4.2.3.Final","netty-4.2.2.Final","netty-4.2.1.Final","netty-4.2.0.Final"],"database_specific":{"source":"https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-100661.json"}}],"schema_version":"1.9.0","severity":[{"type":"CVSS_V4","score":"CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N"}]}