---
id: CVE-2026-23666
title: .NET Framework Denial of Service Vulnerability
summary: >-
  Improper input validation in .NET Framework allows an unauthorized attacker to
  deny service over a network.
severity: high
cvss: 7.5
cvssVector: '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'
cvssSource: cna
cwe:
  - CWE-755
vendor: Microsoft
product: Microsoft .NET Framework 3.5
affected:
  - .net_framework_3.5 >= 3.5.0 < 2.0.50727.8982 & 3.0.30729.8976
  - >-
    .net_framework_3.5_and_4.7.2 >= 4.7.0 < 2.0.50727.9068 & 3.0.30729.9065 &
    4.7.4141.0
  - >-
    .net_framework_3.5_and_4.8 >= 4.8.0 < 2.0.50727.9068 & 3.0.30729.9065 &
    4.8.4801.0
  - >-
    .net_framework_3.5_and_4.8.1 >= 4.8.1 < 2.0.50727.9181 & 3.0.30729.9165 &
    4.8.9332.0
  - .net_framework_4.6.2_4.7_4.7.1_4.7.2 >= 4.7.0 < 4.8.4801.0
  - .net_framework_4.8 >= 4.8.0 < 4.8.4801.0
ssvc:
  exploitation: none
  automatable: 'yes'
  technicalImpact: partial
  timestamp: '2026-04-15T13:40:59.739058Z'
published: '2026-04-14'
updated: '2026-09-25'
sourceUpdated: '2026-09-25T17:25:37.542Z'
source: CVEORG
sourceUrl: 'https://www.cve.org/CVERecord?id=CVE-2026-23666'
references:
  - url: 'https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-23666'
    label: .NET Framework Denial of Service Vulnerability
tags:
  - cve.org
epss: 0.0133
epssPercentile: 0.6982
ingestedAt: '2026-09-25T18:14:20.437Z'
---

## Overview

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

## Affected

- `.net_framework_3.5 >= 3.5.0 < 2.0.50727.8982 & 3.0.30729.8976`
- `.net_framework_3.5_and_4.7.2 >= 4.7.0 < 2.0.50727.9068 & 3.0.30729.9065 & 4.7.4141.0`
- `.net_framework_3.5_and_4.8 >= 4.8.0 < 2.0.50727.9068 & 3.0.30729.9065 & 4.8.4801.0`
- `.net_framework_3.5_and_4.8.1 >= 4.8.1 < 2.0.50727.9181 & 3.0.30729.9165 & 4.8.9332.0`
- `.net_framework_4.6.2_4.7_4.7.1_4.7.2 >= 4.7.0 < 4.8.4801.0`
- `.net_framework_4.8 >= 4.8.0 < 4.8.4801.0`

## Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.