CVE-2026-21218
Microsoft .Net 8.0.0 – 8.0.24
Raw vector
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:NSummary
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, ranked in the top 40% of CVEs by exploit likelihood; it is not currently listed in the CISA KEV catalog.
The strongest mitigations our analysis identified map to SI-10 (Information Input Validation) — see the control section below for these in your framework.
Deeper analysis AI-assisted summary
Synthesised by an AI model from the NVD description and linked references — a reading aid, not an authoritative source.
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.
EU & UK References
- 🇪🇺 ENISA EUVD: EUVD-2026-7347
Vulnerability Data
Improper handling of missing special element in .NET allows an unauthorized attacker to perform spoofing over a network.
- CWE(s)
Related Threats
CVEs Like This One
Affected Assets
Mitigating Controls
Mitigating Controls (NIST 800-53 r5) AI
SI-10 directly requires validation of information inputs, structurally preventing failures to handle missing special elements.
Mitigating Controls (NIST CSF 2.0) AI
Derived directly from the weakness types (CWEs) cited in the NVD entry via our AI-authored CWE→CSF cross-walk (authority under review) — links open the control.
Secure SDLC practices directly prevent improper input-element handling by enforcing validation requirements throughout development.
Identifying and recording vulnerabilities enables remediation of missing-special-element flaws before exploitation.
Mitigating Controls (ISO/IEC 27001:2022 Annex A) AI
Derived directly from the weakness types (CWEs) cited in the NVD entry via our AI-authored CWE→ISO cross-walk (authority under review) — links open the control.
Security testing can discover missing-element flaws but does not prevent them by itself.
Secure SDLC practices can include input validation rules that detect missing special elements.
Application security requirements can mandate handling of missing delimiters or markers in input.
Secure architecture principles may indirectly reduce malformed-input risks but do not specifically address missing elements.
Secure coding standards directly require validation for missing special elements, covering most of this weakness.