CVE-2026-21218
published 2026-02-10CVE-2026-21218: Improper handling of missing special element in .NET allows an unauthorized attacker to perform spoofing over a network.
PriorityP347high7.5CVSS 3.1
AVNACLPRNUINSUCNIHAN
EPSS
1.01%
59.4th percentile
Improper handling of missing special element in .NET allows an unauthorized attacker to perform spoofing over a network.
Affected
15 ranges
| Vendor | Product | Version range | Fixed in |
|---|---|---|---|
| microsoft | net | >= 10.0.0 < 10.0.3 | 10.0.3 |
| microsoft | net | >= 8.0.0 < 8.0.24 | 8.0.24 |
| microsoft | net | >= 9.0.0 < 9.0.13 | 9.0.13 |
| microsoft | net_10.0 | >= 10.0.0 < 10.0.3 | 10.0.3 |
| microsoft | net_8.0 | >= 8.0.0 < 8.0.24 | 8.0.24 |
| microsoft | net_9.0 | >= 9.0.0 < 9.0.13 | 9.0.13 |
| msrc | net_10.0_installed_on_linux | — | — |
| msrc | net_10.0_installed_on_mac_os | — | — |
| msrc | net_10.0_installed_on_windows | — | — |
| msrc | net_8.0_installed_on_linux | — | — |
| msrc | net_8.0_installed_on_mac_os | — | — |
| msrc | net_8.0_installed_on_windows | — | — |
| msrc | net_9.0_installed_on_linux | — | — |
| msrc | net_9.0_installed_on_mac_os | — | — |
| msrc | net_9.0_installed_on_windows | — | — |
CVSS provenance
nvdv3.17.5HIGHCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N
ghsa7.5HIGH
osv7.5HIGH
vendor_msrc7.5HIGH
Stop checking back — get the weekly exploitation signal.
Every Monday: what got weaponized or added to CISA KEV in the last seven days — each CVE cross-linked to its PoC, Nuclei template, and detection rule. Free, one email a week, unsubscribe in one click.
GHSA
Microsoft Security Advisory CVE-2026-21218 | .NET Security Feature Bypass Vulnerability
ghsa·2026-02-10·CVSS 7.5
CVE-2026-21218 [HIGH] CWE-166 Microsoft Security Advisory CVE-2026-21218 | .NET Security Feature Bypass Vulnerability
Microsoft Security Advisory CVE-2026-21218 | .NET Security Feature Bypass Vulnerability
# Microsoft Security Advisory CVE-2026-21218 | .NET Security Feature Bypass Vulnerability
## Executive summary
Microsoft is releasing this security advisory to provide information about a vulnerability in .NET 8.0, .NET 9.0, and .NET 10.0. This advisory also provides guidance on what developers can do to update their applications to remove this vulnerability.
An attacker could exploit this vulnerability by crafting a malicious payload that bypasses the security checks in the affected System.Security.Cryptography.Cose versions, potentially leading to unauthorized access or data manipulation.
## Announcement
Announcement for this issue can be found at https://github.com/dotnet/announcements/issues/3
OSV
CVE-2026-21218: Improper handling of missing special element in
osv·2026-02-10·CVSS 7.5
CVE-2026-21218 [HIGH] CVE-2026-21218: Improper handling of missing special element in
Improper handling of missing special element in .NET allows an unauthorized attacker to perform spoofing over a network.
OSV
Microsoft Security Advisory CVE-2026-21218 | .NET Security Feature Bypass Vulnerability
osv·2026-02-10·CVSS 7.5
CVE-2026-21218 [HIGH] Microsoft Security Advisory CVE-2026-21218 | .NET Security Feature Bypass Vulnerability
Microsoft Security Advisory CVE-2026-21218 | .NET Security Feature Bypass Vulnerability
# Microsoft Security Advisory CVE-2026-21218 | .NET Security Feature Bypass Vulnerability
## Executive summary
Microsoft is releasing this security advisory to provide information about a vulnerability in .NET 8.0, .NET 9.0, and .NET 10.0. This advisory also provides guidance on what developers can do to update their applications to remove this vulnerability.
An attacker could exploit this vulnerability by crafting a malicious payload that bypasses the security checks in the affected System.Security.Cryptography.Cose versions, potentially leading to unauthorized access or data manipulation.
## Announcement
Announcement for this issue can be found at https://github.com/dotnet/announcements/issues/3
Ubuntu
.NET vulnerability
vendor_ubuntu·2026-02-16
CVE-2026-21218 .NET vulnerability
Title: .NET vulnerability
Summary: .NET could be made to bypass security features.
USN 8025-1 fixed a vulnerability in .NET. This update provides the
corresponding fix for Ubuntu 24.04 LTS.
Original advisory details:
Kevin Jones discovered that the System.Security.Cryptography.Cose
component in .NET did not properly handle certain missing special
elements in input data. An attacker could possibly use this issue to
bypass security checks and gain unauthorized access or perform data
manipulation.
Instructions: In general, a standard system update will make all the necessary changes.
Ubuntu
.NET vulnerability
vendor_ubuntu·2026-02-11
CVE-2026-21218 .NET vulnerability
Title: .NET vulnerability
Summary: .NET could be made to bypass security features.
Kevin Jones discovered that the System.Security.Cryptography.Cose component
in .NET did not properly handle certain missing special elements in input
data. An attacker could possibly use this issue to bypass security checks
and gain unauthorized access or perform data manipulation.
Instructions: In general, a standard system update will make all the necessary changes.
Microsoft
.NET Spoofing Vulnerability
vendor_msrc·2026-02-10·CVSS 7.5
CVE-2026-21218 [HIGH] CWE-166 .NET Spoofing Vulnerability
.NET Spoofing Vulnerability
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.
FAQ: 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.
.NET: .NET
Microsoft: Microsoft
Customer Ac
No detection rules found.
No public exploits indexed.
Sophos
February’s Patch Tuesday assumes battle stations
blogs_sophos·2026-02-13
February’s Patch Tuesday assumes battle stations
Akuter Cyberangriff? Fordern Sie Sofort-Hilfe an
Sophos Central
Partner-Portal
Lizenzen & Accounts
Sophos Home
Sophos Central
Sophos-Central-Anmeldung
Sophos KI
Integrationen
Threat Intelligence
Testversion
Endpoint Protection (Next-Gen Antivirus)
EDR – Endpoint Detection and Response
Server Protection
Mobile Security
XDR – Extended Detection and Response
XDR mit Next-Gen SIEM
ITDR – Identity Threat Detection and Response
Next-Gen Firewall (NGFW)
NDR – Network Detection and Response
Netzwerk-Switches
Wireless Access Points
Workspace Protection
Protected Browser
Zero Trust Network Access (ZTNA)
DNS Protection
Email Monitoring System
E-Mail- und Phishing-Schutz
Awareness-Training für Mitarbeitende
Schutz für Cloud Workloads
Cloud Security Posture Management (CSP
Bleepingcomputer
Microsoft February 2026 Patch Tuesday fixes 6 zero-days, 58 flaws
blogs_bleepingcomputer·2026-02-10·CVSS 8.8
[HIGH] Microsoft February 2026 Patch Tuesday fixes 6 zero-days, 58 flaws
## Microsoft February 2026 Patch Tuesday fixes 6 zero-days, 58 flaws
## Lawrence Abrams
25 Elevation of Privilege vulnerabilities
5 Security Feature Bypass vulnerabilities
12 Remote Code Execution vulnerabilities
6 Information Disclosure vulnerabilities
3 Denial of Service vulnerabilities
7 Spoofing vulnerabilities
When BleepingComputer reports on Patch Tuesday security updates, we only count those released by Microsoft today. Therefore, the number of flaws does not include 3 Microsoft Edge flaws fixed earlier this month.
As part of these updates, Microsoft has also begun to roll out updated Secure Boot certificates to replace the original 2011 certificates that are expiring in late June 2026.
"With this update, Windows quality updates include a broad set of targeting data that i
Wiz
CVE-2026-21218 Impact, Exploitability, and Mitigation Steps | Wiz
blogs_wiz·CVSS 7.5
CVE-2026-21218 [HIGH] CVE-2026-21218 Impact, Exploitability, and Mitigation Steps | Wiz
## CVE-2026-21218 :
C# vulnerability analysis and mitigation
Improper handling of missing special element in .NET allows an unauthorized attacker to perform spoofing over a network.
Source : NVD
## 7.5
Score
Published February 10, 2026
Severity HIGH
CNA Score 7.5
Affected Technologies
C#
.NET SDK
Has Public Exploit No
Has CISA KEV Exploit No
CISA KEV Release Date N/A
CISA KEV Due Date N/A
Exploitation Probability Percentile (EPSS) 13.1
Exploitation Probability (EPSS) N/A
Affected packages and libraries
dotnet8
cpe:2.3:a:microsoft:.net
Sources
Alpine 3.20, 3.21, 3.23 Severity HIGH Has Fix Added at: Feb 21, 2026
Alpine 3.22 Severity HIGH Has Fix Added at: Feb 24, 2026
Alpine edge Severity HIGH Has Fix Added at: Feb 12, 2026
Chainguard Has Fix Added at: Feb 24, 2026
Sophos
February’s Patch Tuesday assumes battle stations
blogs_sophos
February’s Patch Tuesday assumes battle stations
Share This
Microsoft on Tuesday released 58 patches affecting 15 product families. Five of the addressed issues, all involving Azure, are considered by Microsoft to be of Critical severity, though only two require urgent attention (more on that below). Fifteen have a CVSS base score of 8.0 or higher, including two with a 9.8 base score. Six are known to be under active exploit in the wild, and three are publicly disclosed (including one not yet known to be under exploit).
At patch time, five CVEs are judged more likely to be exploited in the next 30 days by the company’s estimation, in addition to the six already detected to be so. Various of this month’s issues are amenable to direct detection by Sophos protections, and we include information on those in a table below. The release also
2026-02-10
Published