What is CVE-2026-23666?
Windows TCP/IP IPv6 remote code execution vulnerability caused by an integer overflow in IPv6 fragment reassembly. Reachable from any adjacent network and rated wormable by Microsoft MSRC, allowing unauthenticated attackers to achieve code execution via crafted IPv6 packets.
The record classifies CVE-2026-23666 under weakness class CWE-190. Its CVSS v3 base vector states that the flaw is reachable remotely over the network, needs no prior authentication, needs no user interaction, and has high impact on availability. 10 affected-product entries are recorded, across 1 vendor, listed below. The identifier was first published 197 days ago.
Severity and exploitation probability
- CVSS v3.1 base score
- 9.8 — CRITICAL
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H/E:P/RL:O/RC:C - EPSS (FIRST)
- 1.3% probability of exploitation in the next 30 days, higher than 70.2% of all scored CVEs
- CISA KEV
- Not listed in the CISA Known Exploited Vulnerabilities catalog
- Threadlinqs priority
- 7.7/10 — a Threadlinqs composite of the CVSS base score, the EPSS percentile and public exploit availability
- Published
- 2026-04-14, last modified 2026-09-25
Is CVE-2026-23666 being exploited?
It currently carries a trending score of 23 in the Threadlinqs vulnerability feed.
Affected products and versions
- Microsoft: .Net Framework, Windows Server 2012, Windows 10 1809, Windows 10 21H2, Windows 10 22H2, Windows Server 2022, Windows 11 22H2, Windows 11 23H2, Windows 11 24H2, Windows 11 25H2
How to fix CVE-2026-23666
Vendor advisory: https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-23666. Apply the vendor fix referenced above to every affected product listed in this record, then confirm the running version against the vendor advisory.
Threat activity tracking CVE-2026-23666
2 tracked threats in the Threadlinqs corpus reference CVE-2026-23666, either in the campaign’s CVE list or as an indicator on the campaign record.
- Microsoft April 2026 Patch Tuesday — 163 CVEs / 88 Advisories (CVE-2026-32201 SharePoint Zero-Day Exploited In-The-Wild, CVE-2026-33825 Defender EoP Public PoC, CVE-2026-33824 IKE RCE CVSS 9.8, CVE-2026-33827 TCP/IP Wormable RCE) — CRITICAL · 2026-04-19
- Microsoft April 2026 Patch Tuesday — 167 Flaws, 2 Zero-Days (SharePoint Spoofing CVE-2026-32201 + Defender EoP CVE-2026-33825) — CRITICAL · 2026-04-14
Sources
Enriched from CVE.org, FIRST EPSS. Last verified by Threadlinqs on .