Microsoft Security Advisory CVE-2026-96222 - .NET Spoofing Vulnerability
The source advisory has changed since this explanation was prepared. Check the current technical data and original advisory below.
Executive Summary
Microsoft has issued a security advisory regarding a vulnerability in System.Security.Cryptography.Xml.
KeyInfoX509Data can accept serialized certificate formats containing attacker-controlled chain metadata instead of requiring a plain X.509 certificate, contributing to certificate-forgery and token-spoofing paths.
Announcement
The announcement for this issue is available at https://github.com/dotnet/announcements/issues/474.
CVSS Details
- Version: 3.1
- Severity: High
- Score: 7.4
- Vector:
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:N - Weakness: CWE-295 (Improper Certificate Validation)
Affected Platforms
- Platforms: Windows, Linux, macOS
- Architectures: All
Affected Packages
This vulnerability impacts Microsoft .NET projects using the following affected package versions:
| Package name | Affected version | Patched version |
|---|---|---|
| System.Security.Cryptography.Xml) | >= 8.0.0, <= 8.0.4 | 8.0.5 |
Advisory FAQ
How do I know if I am affected?
If your project utilizes a package version listed under Affected Packages, you are exposed to this vulnerability.
How do I fix the issue?
-
Install the latest version of .NET. If one or more .NET SDKs were installed through Visual Studio, Visual Studio will prompt you to update, which will also update your .NET SDKs.
-
If your application references the vulnerable package, update the package reference to the patched version. You can list installed versions by running the
dotnet --infocommand.
After installing the updated runtime or SDK, restart applications for the changes to take effect.
Additionally, if you have deployed self-contained applications) targeting any affected version, they are also vulnerable and must be recompiled and redeployed.
Other Information
Reporting Security Issues
If you discover a potential security issue in a supported version of .NET, report it to the Microsoft Security Response Center (MSRC) via the MSRC Researcher Portal.). Further details can be found in the MSRC Report an Issue FAQ.).
Security reports submitted through MSRC may qualify for the Microsoft .NET Bounty program. Details, terms, and conditions are available at https://aka.ms/corebounty..
Support
Questions regarding this advisory can be submitted on GitHub within the .NET GitHub organization. Main repositories are located at https://github.com/dotnet/runtime.. The Announcements repository (https://github.com/dotnet/Announcements)) hosts this bulletin as an issue and links to a discussion issue for questions.
Disclaimer
The information provided in this advisory is provided "as is" without warranty of any kind. Microsoft disclaims all warranties, either express or implied, including the warranties of merchantability and fitness for a particular purpose. In no event shall Microsoft Corporation or its suppliers be liable for any damages whatsoever including direct, indirect, incidental, consequential, loss of business profits or special damages, even if Microsoft Corporation or its suppliers have been advised of the possibility of such damages. Some states do not allow the exclusion or limitation of liability for consequential or incidental damages so the foregoing limitation may not apply.
External Links
Acknowledgements
- Vaisha Bernard with Eye Security
Revisions
V1.0 (10/13/2026): Advisory published.
What to do
To resolve this issue:
- Install the latest version of .NET or update via Visual Studio when prompted to ensure the runtime and SDKs are up to date.
- Update package references to
System.Security.Cryptography.Xmlversion 8.0.5 or newer. - Restart applications after updating the runtime or SDK.
- Recompile and redeploy any self-contained applications that target affected versions.
Affected software
Click a technology to see all vulnerabilities affecting it.
| Platform | Package | Vulnerable versions | Fixed in |
|---|---|---|---|
| .NET (NuGet) | System.Security.Cryptography.Xml | >= 8.0.0, < 8.0.5 | 8.0.5 |
References
- https://github.com/dotnet/runtime/security/advisories/GHSA-vrv5-2jg9-4mmr
- https://github.com/dotnet/announcements/issues/474
- https://github.com/dotnet/runtime/issues/135705
- https://github.com/dotnet/runtime
- https://nvd.nist.gov/vuln/detail/CVE-2026-96222
- https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-96222
- CVSS vector
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:N- Weakness (CWE)
CWE-295- Platform
- .NET (NuGet)
- Package
System.Security.Cryptography.Xml- Disclosed
- 13.10.2026
- Updated
- 19.10.2026 22:17
Sources and licenses · Edited or translated by DockRay; source rights and applicable licenses are retained.
OSV / GitHub Advisory Database - GHSA-vrv5-2jg9-4mmr - CC BY 4.0
Vulnerability history: System.Security.Cryptography.Xml
All published vulnerabilities of this package (.NET (NuGet)), newest first. Shows whether this is a one-off slip or a package that needs watching.
- Total entries
- 14
- First → latest
- 10.2018 10.2026
- Without a fix
- 0
- Exploited in attacks
- 0
Severity breakdown
- High 13
- Medium 1
Disclosures per year
- 2018: 2
- 2019: 0
- 2020: 0
- 2021: 0
- 2022: 0
- 2023: 0
- 2024: 1
- 2025: 0
- 2026: 11
-
Microsoft Security Advisory CVE-2026-96222 - .NET Spoofing Vulnerability this entry
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