CVE-2026-75596
Netty: Fragmented ClientHello records trigger quadratic pre-handshake reassembly in default SNI parsing
- Published
- Updated
- Reserved
- Assigned by
- GitHub_M
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.
Scores
| Scored by | CVSS | Score | Vector |
|---|---|---|---|
| GitHub_MCNA (assigner) | 4.0 | High8.7 | 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 |
| NVDNVD · Analyzed | 4.0 | High8.7 | 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/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X |
- EPSS (exploitation in 30 days)
- 0.37% · top 68% of all CVEs (4 Nov 2026)
- CISA SSVC
- Exploitation: none · Automatable: yes · Technical impact: partial
The list uses the assigner's score when there is one, then CISA's, then NVD's: High 8.7.
Weakness
Affected products
Affected packages
From reviewed advisories of the GitHub Advisory Database.
- Mavenio.netty:netty-handlerGHSA-fccg-mwvh-qqg4 (opens in a new tab)
References (7)
- https://github.com/netty/netty/security/advisories/GHSA-fccg-mwvh-qqg4 (opens in a new tab)x_refsource_CONFIRM
- https://github.com/netty/netty/pull/17213 (opens in a new tab)x_refsource_MISC
- https://github.com/netty/netty/pull/17217 (opens in a new tab)x_refsource_MISC
- https://github.com/netty/netty/commit/1b5abc6443b63726c72cdd285af2feb7ddbb8ff7 (opens in a new tab)x_refsource_MISC
- https://github.com/netty/netty/commit/9e0519239108a69b7e9bbc5e9182ee139a0d7961 (opens in a new tab)x_refsource_MISC
- https://github.com/netty/netty/releases/tag/netty-4.1.137.Final (opens in a new tab)x_refsource_MISC
- https://github.com/netty/netty/releases/tag/netty-4.2.17.Final (opens in a new tab)x_refsource_MISC
Sources
The same CVE in the primary databases and aggregators, to check against.
- CVE.org record (opens in a new tab)
- CVE List JSON (GitHub) (opens in a new tab)
- NVD (opens in a new tab)
- FIRST EPSS (opens in a new tab)
- OSV.dev (opens in a new tab)
- GitHub Advisory GHSA-fccg-mwvh-qqg4 (opens in a new tab)
- CIRCL Vulnerability-Lookup (opens in a new tab)
Badge for a README or a ticket
[](https://trackcve.app/cve/CVE-2026-75596)Record last updated .