CVE-2026-75596
Fragmented TLS ClientHello causes quadratic CPU in Netty, enabling DoS.
Is CVE-2026-75596 being exploited?
Not confirmed. CVE-2026-75596 does not appear in CISA's Known Exploited Vulnerabilities catalog, which records only exploitation that has been observed and reported publicly. That is evidence of absence of a report, not evidence the flaw is unattacked. EPSS currently estimates a 0.35% probability of exploitation in the next 30 days.
How severe is CVE-2026-75596?
CVE-2026-75596 is rated High with a CVSS score of 8.7. Severity describes how bad exploitation would be, not how likely it is: pair it with exploitation evidence before deciding what to patch first.
Is there a patch for CVE-2026-75596?
Yes. A fix has been recorded for CVE-2026-75596. The vendor advisory is the authority on the exact fixed version — apply it from there rather than from a summary.
What does CVE-2026-75596 affect?
CVE-2026-75596 affects Netty < 4.1.137.Final, Netty < 4.2.17.Final, Java applications using io.netty.handler.ssl.SniHandler. Confirm the exact affected versions against the vendor advisory before deciding you are exposed.
What should I do about CVE-2026-75596?
Upgrade to Netty 4.1.137.Final or 4.2.17.Final; implement TLS rate-limits.
Exploitation status reflects CISA's KEV catalog as we last synced it. Check the catalog directly.
Unauthenticated remote attacker can send many tiny TLS records of a large ClientHello causing quadratic CPU per connection, degrading services or causing event-loop DoS.
Patch when possible
- affected< 4.1.137.Final
- affected>= 4.2.0.Final and < 4.2.17.Final
As published in the CVE Program record. A version outside these ranges is not a statement that it is unaffected — vendors sometimes understate a range, and distribution-backported builds carry upstream numbers that do not reflect what was patched into them.