CVE-2026-21218
Published: 10 February 2026
Summary
CVE-2026-21218 is a high-severity Improper Handling of Missing Special Element (CWE-166) vulnerability in Microsoft .Net. Its CVSS base score is 7.5 (High).
Operationally, exploitation aligns with the MITRE ATT&CK technique Exploit Public-Facing Application (T1190); ranked at the 13.7th percentile by exploit likelihood (below the median); it is not currently listed in the CISA KEV catalog.
Threat & Defense at a Glance
Threat & Defense Details
MITRE ATT&CK Enterprise TechniquesAI
Why these techniques?
Network-exploitable spoofing flaw (no auth/UI) directly enables public app exploitation (T1190) and adversary-in-the-middle spoofing (T1557).
NVD Description
Improper handling of missing special element in .NET allows an unauthorized attacker to perform spoofing over a network.
Deeper analysisAI
CVE-2026-21218 is a vulnerability in .NET stemming from improper handling of a missing special element. This flaw enables an unauthorized attacker to perform spoofing over a network. The issue carries a CVSS v3.1 base score of 7.5 (AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N) and is classified under CWE-166.
Any unauthenticated attacker with network access can exploit this vulnerability due to its low attack complexity and lack of required privileges or user interaction. Successful exploitation allows the attacker to achieve spoofing, resulting in a high impact on integrity while causing no impact on confidentiality or availability.
The Microsoft Security Response Center advisory provides details on mitigation and patches at https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-21218.
Details
- CWE(s)