Threat Intelligence / CVE / CVE-2026-23666

CVE-2026-23666 — Microsoft .Net Framework

CVSS v3.1 9.8 (CRITICAL) · EPSS 0.1% (higher than 35.4% of all scored CVEs) · Priority 6.3/10 · Published 2026-04-14

As of 2026-05-07, CVE-2026-23666 is a CRITICAL-severity vulnerability in Microsoft .Net Framework, CVSS v3.1 9.8, EPSS 0.1% (35.4th percentile). Threadlinqs Intelligence links 2 tracked threat campaigns to CVE-2026-23666, most recently “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)”.

Last updated: 2026-05-07

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 151 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)
0.1% probability of exploitation in the next 30 days, higher than 35.4% of all scored CVEs
CISA KEV
Not listed in the CISA Known Exploited Vulnerabilities catalog
Threadlinqs priority
6.3/10 — a Threadlinqs composite of the CVSS base score, the EPSS percentile and public exploit availability
Published
2026-04-14, last modified 2026-05-07

Is CVE-2026-23666 being exploited?

It currently carries a trending score of 14 in the Threadlinqs vulnerability feed.

Affected products and versions

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.

Sources

Seeded from threat-derived and not yet processed by the Threadlinqs enrichment pipeline, so blank CVSS, EPSS or KEV fields above mean NOT MEASURED rather than measured-absent.

Full detection coverage & IOCs for threats exploiting CVE-2026-23666 are available via the Threadlinqs MCP server (Purple tier). View plans →

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