What’s Vulnerable › Vulnerabilities

CVE-2021-26423: .NET Core and Visual Studio Denial of Service Vulnerability

• Severity: medium (CVSS 5.0 v2.0)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 3.9% probability of exploitation in the next 30 days
• Public exploit or detection template: none known
• Published: 2021-08-12 · updated 2026-08-10

Description

.NET Core and Visual Studio Denial of Service Vulnerability

Affected products

• Microsoft .NET: from 5.0 through 5.0.8
• Microsoft Corporation .NET Core: from 2.1 through 2.1.28; from 3.1 through 3.1.17
• Microsoft PowerShell Core: from 7.0 before 7.0.7; from 7.1 before 7.1.4 — fixed in 7.0.7, 7.1.4
• Microsoft Visual Studio 2017 version 15.9 (includes 15.0 - 15.8): from 15.0 through 15.9
• Microsoft Visual Studio 2019: from 16.0 through 16.10; 8.10
• Microsoft .NET 5.0: from 5.0.0 before 5.0.9 — fixed in 5.0.9
• Microsoft .NET Core 2.1: from 2.1 before 2.1.30 — fixed in 2.1.30
• Microsoft .NET Core 3.1: from 3.1 before 3.1.18 — fixed in 3.1.18
• Microsoft Visual Studio 2019 version 16.10 (includes 16.0 - 16.9): from 16.10.0 before 16.10.5 — fixed in 16.10.5
• Microsoft Visual Studio 2019 version 16.4 (includes 16.0 - 16.3): from 16.0 before 16.4.25 — fixed in 16.4.25
• Microsoft Visual Studio 2019 version 16.7 (includes 16.0 – 16.6): from 16.0.0 before 16.7.18 — fixed in 16.7.18
• Microsoft Visual Studio 2019 version 16.9 (includes 16.0 - 16.8): from 15.0.0 before 16.9.10 — fixed in 16.9.10
• Microsoft PowerShell Core 7.0: from 7.0.0 before 7.0.7 — fixed in 7.0.7
• Microsoft PowerShell Core 7.1: from 7.1.0 before 7.1.4 — fixed in 7.1.4
• Microsoft Visual Studio 2017 version 15.9 (includes 15.0 - 15.8): from 15.9.0 before 15.9.38 — fixed in 15.9.38
• Microsoft Visual Studio 2019 for Mac version 8.10: from 8.1.0 before 8.10.7 — fixed in 8.10.7

How to fix

Upgrade to a fixed version: Microsoft PowerShell Core 7.0.7, 7.1.4; Microsoft .NET 5.0 5.0.9; Microsoft .NET Core 2.1 2.1.30; Microsoft .NET Core 3.1 3.1.18; Microsoft Visual Studio 2019 version 16.10 (includes 16.0 - 16.9) 16.10.5; Microsoft Visual Studio 2019 version 16.4 (includes 16.0 - 16.3) 16.4.25; Microsoft Visual Studio 2019 version 16.7 (includes 16.0 – 16.6) 16.7.18; Microsoft Visual Studio 2019 version 16.9 (includes 16.0 - 16.8) 16.9.10; Microsoft PowerShell Core 7.0 7.0.7; Microsoft PowerShell Core 7.1 7.1.4; Microsoft Visual Studio 2017 version 15.9 (includes 15.0 - 15.8) 15.9.38; Microsoft Visual Studio 2019 for Mac version 8.10 8.10.7. Check the vendor advisory for mitigations.

References

• https://msrc.microsoft.com/update-guide/vulnerability/CVE-2021-26423
• https://portal.msrc.microsoft.com/en-US/security-guidance/advisory/CVE-2021-26423

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