Microsoft Security Advisory CVE-2026-96959 - .NET and Visual Studio Denial of Service Vulnerability
The source advisory has changed since this explanation was prepared. Check the current technical data and original advisory below.
Executive summary
Microsoft is releasing this security advisory to provide information about a vulnerability in System.Security.Cryptography.Xml; System.Private.Xml. This advisory also provides guidance on what developers can do to update their applications to remove this vulnerability.
Signed XML fixes add input-depth and operation-count limits, prohibit DTD processing by default, validate entity references, bound encrypted-data candidate processing, and cap attributes and namespaces used by C14N transforms.
Announcement
Announcement for this issue can be found at https://github.com/dotnet/announcements/issues/489
CVSS Details
- Version: 3.1
- Severity: High
- Score: 7.5
- Vector:
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H - Weakness: CWE-770 (Allocation of Resources Without Limits or Throttling)
Affected Platforms
- Platforms: Windows, Linux, macOS
- Architectures: All
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 | >= 10.0.0, <= 10.0.12 | 10.0.13 |
| System.Security.Cryptography.Xml | >= 11.0.0-preview.1, <= 11.0.0-rc.1 | 11.0.0-rc.2 |
| System.Security.Cryptography.Xml | >= 8.0.0, <= 8.0.4 | 8.0.5 |
| System.Security.Cryptography.Xml | >= 9.0.0, <= 9.0.20 | 9.0.21 |
Advisory FAQ
How do I know if I am affected?
If using a package listed in affected packages, you're exposed to the vulnerability.
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
Acknowledgements
- novice-22
- Ky0toFu (@ky0tofu)
- Dr.-Ing Ashar Javed (@soaj1664ashar)
Revisions
V1.0 (10/13/2026): Advisory published.
What to do
-
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 --infocommand.
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.
Affected software
Click a technology to see all vulnerabilities affecting it.
| Platform | Package | Vulnerable versions | Fixed in |
|---|---|---|---|
| .NET (NuGet) | System.Security.Cryptography.Xml | >= 10.0.0, < 10.0.13, >= 11.0.0-preview.1, < 11.0.0-rc.2, >= 8.0.0, < 8.0.5, >= 9.0.0, < 9.0.21 | 10.0.13, 11.0.0-rc.2, 8.0.5, 9.0.21 |
References
- https://github.com/dotnet/runtime/security/advisories/GHSA-c399-9853-6jmj
- https://github.com/dotnet/announcements/issues/489
- https://github.com/dotnet/runtime/issues/135710
- https://github.com/dotnet/runtime
- https://nvd.nist.gov/vuln/detail/CVE-2026-96959
- https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-96959
- CVSS vector
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H- Weakness (CWE)
CWE-770- 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-c399-9853-6jmj - 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
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Microsoft Security Advisory CVE-2026-96959 - .NET and Visual Studio Denial of Service Vulnerability this entry
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