CVE-2026-75596: netty · Inefficient Algorithmic Complexity
Affects nettySource GCVE Database
Not known to be exploited · CVSS 8.7 High : upgrade to 4.2.17.Final or 4.1.137.Final soon.
Data as of 26 Oct 2026, 17:16 UTC
- EPSS
- 0.3% chance of exploitation in 30 days – higher than 31% of CVEsExploit Prediction Scoring System: the likelihood attackers will use this flaw soon.
- Patch
- Available – fixed in 4.2.17.Final, 4.1.137.Final
CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:NExploitation evidence
Disclosed: evidence found.
CVE published 19 Aug 2026
Detectable: no evidence on record.
No public nuclei template indexed
Weaponised: no evidence on record.
No public exploit code indexed in Metasploit or Exploit-DB
Exploited in the wildExploited: no evidence on record.
Not in CISA KEV and no source reports exploitation
Observed by OffSeq MirageSeen by Mirage: no evidence on record.
No attack traffic recorded by OffSeq Mirage sensors
A missing step is not evidence of safety. Sources: cve.org (opens in a new tab), the Metasploit, Exploit-DB and nuclei-templates index as of 26 Oct 2026.
What to do
Upgrade netty to 4.2.17.Final or 4.1.137.Final.
Affected software
| Product | Affected | Fixed in |
|---|---|---|
| netty netty | Affected
| Fixed in
|
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.
References
- github.com/netty/netty/security/advisories/GHSA-fccg-mwvh-qqg4 (opens in a new tab)
- github.com/netty/netty/pull/17213 (opens in a new tab)
- github.com/netty/netty/pull/17217 (opens in a new tab)
- github.com/netty/netty/commit/1b5abc6443b63726c72cdd285af2feb7ddbb8ff7 (opens in a new tab)
- github.com/netty/netty/commit/9e0519239108a69b7e9bbc5e9182ee139a0d7961 (opens in a new tab)
- github.com/netty/netty/releases/tag/netty-4.1.137.Final (opens in a new tab)
- github.com/netty/netty/releases/tag/netty-4.2.17.Final (opens in a new tab)