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CVE-2026-23666 is a denial-of-service vulnerability in Microsoft .NET Framework, including affected .NET Framework 3.5 and 4.8.1 deployments referenced in Microsoft's April 14, 2026 security update for Microsoft server operating system version 23H2. The issue is described as improper input validation and more specifically as a race condition caused by improper synchronization during concurrent execution using shared resources. An unauthorized attacker can exploit this flaw over the network to trigger a service disruption condition in affected .NET Framework systems.
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What it means. What to do now. Patch path, mitigations, and the assume-compromise checklist.
What an attacker gets, and what they’ve been doing with it.
If you can’t patch tonight, do this now.
Patch, then assume compromise.
No public exploits tracked yet. Mallory keeps watching.
No public exploit code observed for this vulnerability.
Products and vendors Mallory has correlated with this vulnerability. Open in Mallory to drill down to specific CPE configurations and version ranges.
Vendor-confirmed product mapping. Mallory continuously reconciles this list against your asset inventory.
6 sources tracked across advisories, community write-ups, and news. New activity surfaces here as Mallory finds it.
A critical denial-of-service vulnerability in the .NET Framework caused by a race condition.
A critical denial-of-service vulnerability in the .NET Framework that can be exploited over the network.
A denial-of-service vulnerability in .NET Framework addressed by the April 14, 2026 Microsoft security update for server operating system version 23H2.
Query your assets running an affected version, and investigate the blast radius.
Every observed campaign linking this CVE to a named adversary.
Malware families riding this exploit, with evidence and IOCs.
YARA, Sigma, Snort, and vendor rules, auto-deployed to your SIEM.
Cross-references every affected SKU, including bundled OEM variants.
Community discussion across Reddit, Mastodon, and other social sources.