CVE-2026-23666: .NET Framework Denial of Service Vulnerability

Severity: high (CVSS 7.5 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 1.3% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2026-04-14 · updated 2026-10-26
Weakness: CWE-755

Description

Improper input validation in .NET Framework allows an unauthorized attacker to deny service over a network.

Affected products

Microsoft .NET Framework: 3.5, 4.7.2, 4.8, 4.8.1, 4.6.2, 4.7 (+1)
Microsoft .NET Framework 3.5: from 3.5.0 before 2.0.50727.8982 & 3.0.30729.8976 — fixed in 2.0.50727.8982 & 3.0.30729.8976
Microsoft .NET Framework 3.5 AND 4.7.2: from 4.7.0 before 2.0.50727.9068 & 3.0.30729.9065 & 4.7.4141.0 — fixed in 2.0.50727.9068 & 3.0.30729.9065 & 4.7.4141.0
Microsoft .NET Framework 3.5 AND 4.8: from 4.8.0 before 2.0.50727.9068 & 3.0.30729.9065 & 4.8.4801.0 — fixed in 2.0.50727.9068 & 3.0.30729.9065 & 4.8.4801.0
Microsoft .NET Framework 3.5 AND 4.8.1: from 4.8.1 before 2.0.50727.9181 & 3.0.30729.9165 & 4.8.9332.0 — fixed in 2.0.50727.9181 & 3.0.30729.9165 & 4.8.9332.0
Microsoft .NET Framework 4.6.2/4.7/4.7.1/4.7.2: from 4.7.0 before 4.8.4801.0 — fixed in 4.8.4801.0
Microsoft .NET Framework 4.8: from 4.8.0 before 4.8.4801.0 — fixed in 4.8.4801.0

How to fix

Upgrade to a fixed version: Microsoft .NET Framework 3.5 2.0.50727.8982 & 3.0.30729.8976; Microsoft .NET Framework 3.5 AND 4.7.2 2.0.50727.9068 & 3.0.30729.9065 & 4.7.4141.0; Microsoft .NET Framework 3.5 AND 4.8 2.0.50727.9068 & 3.0.30729.9065 & 4.8.4801.0; Microsoft .NET Framework 3.5 AND 4.8.1 2.0.50727.9181 & 3.0.30729.9165 & 4.8.9332.0; Microsoft .NET Framework 4.6.2/4.7/4.7.1/4.7.2 4.8.4801.0; Microsoft .NET Framework 4.8 4.8.4801.0. Check the vendor advisory for mitigations.

References

Get alerted when CVE-2026-23666 or the next vulnerability affects your stack