CVE-2026-21218: .NET Spoofing Vulnerability

Overview

Severity
High (CVSS 7.5)
CVSS Vector
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N/E:U/RL:O/RC:C
Category
Spoofing
Exploit Status
Not Exploited
Exploitation Likelihood
Unlikely
Patch Tuesday
2026-Feb
Released
2026-02-10
EPSS Score
0.04% (percentile: 13.3%)

Description

Improper handling of missing special element in .NET allows an unauthorized attacker to perform spoofing over a network.

FAQ

According to the CVSS metric, the privileges required is none (PR:N). What does that mean for this vulnerability? The score is based on no user account is needed to perform the attack. According to the CVSS metrics, successful exploitation of this vulnerability could lead to no loss of confidentiality (C:N) and availability (A:L), but could lead to major loss of integrity (I:H). What does that mean for this vulnerability? An attacker who successfully exploited this vulnerability could bypass critical-header validation and the service may accept a message it should reject.

Affected Products (9)

Developer Tools

  • .NET 10.0 installed on Mac OS
  • .NET 10.0 installed on Windows
  • .NET 8.0 installed on Linux
  • .NET 8.0 installed on Windows
  • .NET 10.0 installed on Linux
  • .NET 8.0 installed on Mac OS
  • .NET 9.0 installed on Mac OS
  • .NET 9.0 installed on Linux
  • .NET 9.0 installed on Windows

Security Updates (3)

Acknowledgments

<a href="https://github.com/vcsjones">vcsjones</a> with GitHub

Revision History

  • 2026-02-10: Information published.