How severe is CVE-2026-96222?

CVE-2026-96222 has a CVSS score of 7.4/10, rated HIGH. Immediate patching is strongly recommended.

Which packages are affected by CVE-2026-96222?

CVE-2026-96222 affects the following packages: System.Security.Cryptography.Xml (NuGet). Ecosystems affected: NuGet.

How do I fix CVE-2026-96222?

Update System.Security.Cryptography.Xml to 8.0.5 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-96222 is resolved across your whole dependency graph.

How do I detect CVE-2026-96222 in my NuGet dependencies?

Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for System.Security.Cryptography.Xml, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.

How do I mitigate CVE-2026-96222 if there is no patch (or I can't update yet)?

If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.

Is CVE-2026-96222 actively exploited in the wild?

No public exploit code has been indexed for CVE-2026-96222 yet. This does not mean the vulnerability cannot be exploited — absence of public exploits does not imply safety. Apply the recommended fix and use O3 Security to monitor your exposure.

When was CVE-2026-96222 published, and has it been updated?

CVE-2026-96222 was published on October 13, 2026 and was last updated on October 13, 2026. Advisory data evolves as severity scores, affected ranges, and exploit intelligence are revised — always check the latest version of the advisory before acting.

.NET

.NET NuGet

Not in CISA KEV

HIGH severity

CVE-2026-96222 — System.Security.Cryptogra…

HIGH

CVE-2026-96222 is a high-severity (CVSS 7.4) vulnerability in System.Security.Cryptography.Xml. A fix is available for System.Security.Cryptography.Xml — see the affected versions and patch details below.

Microsoft Security Advisory CVE-2026-96222 - .NET Spoofing Vulnerability

Published

Oct 13, 2026

Updated

Oct 13, 2026

Affected

1 pkg

Patched

1 / 1

Exploits

None indexed

Exploitation data as of Oct 13, 2026 · OSV.dev, FIRST.org (EPSS)

Real-World Exposure

1 pkg affected

.NETSystem.Security.Cryptography.Xml

Real-time download stats are indexed for npm and PyPI packages. This vulnerability affects NuGet packages — download data is not available via public APIs for these ecosystems.

Description

Executive summary

Microsoft is releasing this security advisory to provide information about a vulnerability in System.Security.Cryptography.Xml. This advisory also provides guidance on what developers can do to update their applications to remove this vulnerability.

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

Announcement for this issue can be found 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

<a name="affected-packages"></a>Affected Packages

The vulnerability affects Microsoft .NET projects that use an affected package version listed below.

Package name	Affected version	Patched version
System.Security.Cryptography.Xml	>= 8.0.0, <= 8.0.4	8.0.5

Advisory FAQ

<a name="how-affected"></a>How do I know if I am affected?

If using a package listed in affected packages, you're exposed to the vulnerability.

<a name="how-fix"></a>How do I fix the issue?

To fix the issue please install the latest version of .NET. If you have installed one or more .NET SDKs through Visual Studio, Visual Studio will prompt you to update Visual Studio, 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 the versions you have installed by running the dotnet --info command.

Once you have installed the updated runtime or SDK, restart your apps for the update to take effect.

Additionally, if you've deployed self-contained applications targeting any of the impacted versions, these applications are also vulnerable and must be recompiled and redeployed.

Other Information

Reporting Security Issues

If you have found a potential security issue in a supported version of .NET, please report it to the Microsoft Security Response Center (MSRC) via the MSRC Researcher Portal. Further information can be found in the MSRC Report an Issue FAQ.

Security reports made through MSRC may qualify for the Microsoft .NET Bounty. Details of the Microsoft .NET Bounty Program including terms and conditions are at https://aka.ms/corebounty.

Support

You can ask questions about this issue on GitHub in the .NET GitHub organization. The main repos are located at https://github.com/dotnet/runtime. The Announcements repo (https://github.com/dotnet/Announcements) will contain this bulletin as an issue and will include a link to a discussion issue. You can ask questions in the linked discussion issue.

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

CVE-2026-96222

Acknowledgements

Vaisha Bernard with Eye Security

Revisions

V1.0 (10/13/2026): Advisory published.

Affected Packages

1 total 1 fixed

Ecosystem	Package	Vulnerable range	Fix
.NETNuGet	`System.Security.Cryptography.Xml`	≥ 8.0.0&&< 8.0.5	8.0.5`dotnet add package System.Security.Cryptography.Xml --version 8.0.5`

Detection & mitigation playbook

Open-source dependency

Detect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for System.Security.Cryptography.Xml, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update System.Security.Cryptography.Xml to 8.0.5 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-96222 is resolved across your whole dependency graph.
Workarounds
If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.

Frequently Asked Questions

## Executive summary Microsoft is releasing this security advisory to provide information about a vulnerability in System.Security.Cryptography.Xml. This advisory also provides guidance on what developers can do to update their applications to remove this vulnerability. `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 Announcement for this issue can be found at https://github.com/dotnet/announcements/issues/47

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