CVE-2026-75596Netty: Fragmented ClientHello records trigger quadratic pre-handshake reassembly in default SNI parsing
Updated under an hour ago ()
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No exploitation reported and no EPSS estimate yet.
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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
- 8.7 HIGH (v4.0, CNA)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
- Weakness (CWE)
- CWE-407
- Known exploited
- Not in CISA's KEV catalog
- EPSS (exploitation in the next 30 days)
- Not loaded for this CVE
- Assigned by
- GitHub_M
- NVD analysis
- Analyzed
- Record last updated
- Aug 20, 2026
- First seen by InfoSec Signals
- Oct 9, 2026
Affected products
netty netty netty:netty (from the name) | before 4.1.137.Final; from 4.2.0.Final, < 4.2.17.Final | CNA record |
netty netty netty:netty | before 4.1.137; from 4.2.0 before 4.2.17 | NVD |
References
- https://github.com/netty/netty/security/advisories/GHSA-fccg-mwvh-qqg4x-refsource-confirm, vendor-advisory
- https://github.com/netty/netty/pull/17213x-refsource-misc, issue-tracking, patch
- https://github.com/netty/netty/pull/17217x-refsource-misc, issue-tracking, patch
- https://github.com/netty/netty/commit/1b5abc6443b63726c72cdd285af2feb7ddbb8ff7x-refsource-misc, patch
- https://github.com/netty/netty/commit/9e0519239108a69b7e9bbc5e9182ee139a0d7961x-refsource-misc, patch
- https://github.com/netty/netty/releases/tag/netty-4.1.137.Finalx-refsource-misc, release-notes
- https://github.com/netty/netty/releases/tag/netty-4.2.17.Finalx-refsource-misc, release-notes
The CVE record on cve.org NVD's entry
The CVE record is authoritative. Products marked “from the name” were identified from the CNA's free-text names, not a CPE, and are matched less certainly. This product uses the NVD API but is not endorsed or certified by the NVD.