{"cve":"CVE-2026-75596","nvd":{"published":"2026-08-19T21:17:37.740","modified":"2026-10-26T10:10:00.140","status":"Analyzed","description":"Netty is an asynchronous, event-driven network application framework. Prior to 4.1.137.Final and 4.2.17.Final, the default io.netty.handler.ssl.SniHandler constructors use the pre-handshake ClientHello aggregation path in handler/src/main/java/io/netty/handler/ssl/SslClientHelloHandler.java at io.netty.handler.ssl.SslClientHelloHandler#decode, where handshakeBuffer.clear() and writeBytes() recopy all previously received body bytes for every additional TLS record. An unauthenticated remote peer can advertise a large ClientHello and deliver its body in thousands of tiny records, causing quadratic CPU work on the event loop before the TLS handshake completes and degrading TLS handling for other clients. This issue is fixed in versions 4.1.137.Final and 4.2.17.Final.","cvss_v4":{"vector":"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","score":8.7},"cvss_v3":{"version":"3.1","vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H","score":7.5},"cwes":["CWE-407"],"references":["https://github.com/netty/netty/commit/1b5abc6443b63726c72cdd285af2feb7ddbb8ff7","https://github.com/netty/netty/commit/9e0519239108a69b7e9bbc5e9182ee139a0d7961","https://github.com/netty/netty/pull/17213","https://github.com/netty/netty/pull/17217","https://github.com/netty/netty/releases/tag/netty-4.1.137.Final"],"products":["netty:netty"],"source":"nvd","synced_at":"2026-10-26T10:28:23.151169805+00:00"},"epss":{"cve":"CVE-2026-75596","score":0.00374,"percentile":0.31069,"date":"2026-10-25"},"kev":null,"osv":[{"id":"GHSA-fccg-mwvh-qqg4","url":"https://osv.dev/vulnerability/GHSA-fccg-mwvh-qqg4","summary":"Netty: Fragmented ClientHello records trigger quadratic pre-handshake reassembly in default SNI parsing","modified":"2026-09-08T18:27:48.113951573Z","packages":[{"ecosystem":"Maven","name":"io.netty:netty-handler","purl":"pkg:maven/io.netty/netty-handler","ranges":[">=4.2.0.Final <4.2.17.Final"],"fixed":["4.2.17.Final"]},{"ecosystem":"Maven","name":"io.netty:netty-handler","purl":"pkg:maven/io.netty/netty-handler","ranges":["<4.1.137.Final"],"fixed":["4.1.137.Final"]}]}],"attribution":["This product uses the NVD API but is not endorsed or certified by the NVD.","EPSS scores: FIRST Exploit Prediction Scoring System, https://www.first.org/epss","Known exploited vulnerabilities: CISA Known Exploited Vulnerabilities Catalog, https://www.cisa.gov/known-exploited-vulnerabilities-catalog","Package advisories: OSV (https://osv.dev), from the GitHub Advisory Database, PyPA, Go, RustSec and other ecosystem databases, under CC-BY 4.0 or CC0","CVE records: the CVE Program's CVE List (https://www.cve.org), under its terms of use (https://www.cve.org/Legal/TermsOfUse). CVE is a registered trademark of The MITRE Corporation; this product is not affiliated with the CVE Program."]}