Improper Handling of Missing Special Element in Microsoft products - CVE-2026-21218

Vulnerability identifier: #VU122602

CSH Severity: Medium

CVSS v4: 8.7 [CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:H/VA:N/SC:N/SI:N/SA:N]

CVE-ID: CVE-2026-21218

CWE-ID: CWE-166

Exploitation vector: Remote access

Exploit availability: No public exploit available

The vulnerability allows a remote attacker to compromise the target system.

The vulnerability exists due to improper handling of missing special element in .NET. A remote attacker can perform spoofing attack on the system.

.NET for macOS
.NET for Linux
.NET
Ubuntu
dotnet10 (Ubuntu package)

Install updates from vendor's website.

.NET for macOS - addressed in versions 8.0.24 8.0.24, 9.0.13 9.0.13
.NET for Linux - addressed in versions 8.0.24 8.0.24, 9.0.13 9.0.13
.NET - addressed in versions 8.0.24 8.0.24, 9.0.13 9.0.13
dotnet10 (Ubuntu package) - addressed in versions 8.0.24-0ubuntu1~22.04.1, 8.0.24-0ubuntu1~24.04.1, 8.0.24-0ubuntu1~25.10.1, 8.0.124-0ubuntu1~22.04.1, 8.0.124-0ubuntu1~24.04.1, 8.0.124-0ubuntu1~25.10.1, 8.0.124-8.0.24-0ubuntu1~22.04.1, 8.0.124-8.0.24-0ubuntu1~24.04.1, 8.0.124-8.0.24-0ubuntu1~25.10.1, 9.0.13-0ubuntu1~25.10.1, 9.0.114-0ubuntu1~25.10.1, 9.0.114-9.0.13-0ubuntu1~25.10.1, 10.0.3-0ubuntu1~24.04.1, 10.0.3-0ubuntu1~25.10.1, 10.0.103-0ubuntu1~24.04.1, 10.0.103-0ubuntu1~25.10.1, 10.0.103-10.0.3-0ubuntu1~24.04.1, 10.0.103-10.0.3-0ubuntu1~25.10.1

• https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-21218

• Improper Handling of Missing Special Element in Microsoft .NET
• Ubuntu update for dotnet10
• Ubuntu update for dotnet10