GHSA-w3x6-4m5h-cxqf BIT-dotnet-2026-26171 BIT-dotnet-sdk-2026-26171 BIT-powershell-2026-26171 CVE-2026-26171

Microsoft Security Advisory CVE-2026-26171 – .NET Denial of Service Vulnerability

High NuGet

Severity: 7.5 / 10; High · CVSS 3.1
Exploit chance (EPSS): 1.75%; Chance of exploitation in the next 30 days. Higher than 77.92% of scored vulnerabilities.
Known exploited: No; Not in CISA's catalog
Weakness: CWE-400 Uncontrolled Resource Consumption; CWE-611 Improper Restriction of XML External Entity Reference
Fix: 10.0.6; Upgrade System.Security.Cryptography.Xml to this version or later

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.

A vulnerability exists in EncryptedXml class where uncontrolled resource consumption can give an attacker to the ability to perform a Denial of Service attack.

Announcement

Announcement for this issue can be found at https://github.com/dotnet/announcements/issues/389

CVSS Details

Version: 3.1
Severity: High
Score: 7.5
Vector: 7.5: AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H E:U/RL:O/RC:C
Weakness: CWE-400 CWE-611: Uncontrolled Resource Consumption Improper Restriction of XML External Entity Reference

Affected Platforms

Platforms: All
Architectures: All

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

The vulnerability affects any Microsoft .NET project if it uses any of affected packages versions listed below

<a name=".NET 10"></a>.NET 10

Package name	Affected version	Patched version
System.Security.Cryptography.xml	>=10.0.0, <=10.0.5;	10.0.6

<a name=".NET 9"></a>.NET 9

Package name	Affected version	Patched version
System.Security.Cryptography.xml	>=9.0.0, <=9.0.14;	9.0.15

<a name=".NET 8"></a>.NET 8

Package name	Affected version	Patched version
System.Security.Cryptography.xml	>=8.0.0, <=8.0.2;	8.0.3

Advisory FAQ

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

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

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

To update the Using the System.Security.Cryptography.Xml NuGet package, use one of the following methods:

NuGet Package Manager UI in Visual Studio:

Open your project in Visual Studio.
Right-click on your project in Solution Explorer and select "Manage NuGet Packages..." or navigate to "Project > Manage NuGet Packages".
In the NuGet Package Manager window, select the "Updates" tab. This tab lists packages with available updates from your configured package sources.
Select the package(s) you wish to update. You can choose a specific version from the dropdown or update to the latest available version.
Click the "Update" button.

Using the NuGet Package Manager Console in Visual Studio:

Open your project in Visual Studio.
Navigate to "Tools > NuGet Package Manager > Package Manager Console".
To update a specific package to its latest version, use the following Update-Package command:

Update-Package -Id System.Security.Cryptography.xml

Using the .NET CLI (Command Line Interface):

Open a terminal or command prompt in your project's directory.
To update a specific package to its latest version, use the following add package command:

dotnet add package System.Security.Cryptography.Xml

Once you have updated the nuget package reference you must recompile and deploy your application. Additionally we recommend you update your runtime and/or SDKs, but it is not necessary to patch 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

CVE-2026-26171

Acknowledgements

Ludvig Pedersen

Revisions

V1.0 (April 14, 2026): Advisory published.

Affected versions

NuGet

Package	Vulnerable	Fixed in
System.Security.Cryptography.Xml	`>= 10.0.0, < 10.0.6`	`10.0.6`
System.Security.Cryptography.Xml	`>= 9.0.0, < 9.0.15`	`9.0.15`
System.Security.Cryptography.Xml	`>= 8.0.0, < 8.0.3`	`8.0.3`

How to fix

Move to the fixed version or later with your package manager, update the lockfile, and run your tests. If the package only arrives through another dependency, upgrade that dependency first. If none of its releases pulls a fixed version yet, force the version with your package manager's override.

System.Security.Cryptography.Xml NuGet → `10.0.6`

dotnet

dotnet add package System.Security.Cryptography.Xml --version 10.0.6

Severity breakdown

CVSS 3.1 7.5

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

Attack vector: Network
Attack complexity: Low
Privileges required: None
User interaction: None
Scope: Unchanged
Confidentiality: None
Integrity: None
Availability: High

Weakness

CWE-400: Uncontrolled Resource Consumption

The product does not properly control the allocation and maintenance of a limited resource.

How to prevent it

Architecture and Design: Design throttling mechanisms into the system architecture. The best protection is to limit the amount of resources that an unauthorized user can cause to be expended. A strong authentication and access control model will help prevent such attacks from occurring in the first place. The login application should be protected against DoS attacks as much as possible. Limiting the database access, perhaps by caching result sets, can help minimize the resources expended. To further limit the potential for a DoS attack, consider tracking the rate of requests received from users and blocking requests that exceed a defined rate threshold.
Architecture and Design: Mitigation of resource exhaustion attacks requires that the target system either: recognizes the attack and denies that user further access for a given amount of time, or uniformly throttles all requests in order to make it more difficult to consume resources more quickly than they can again be freed. The first of these solutions is an issue in itself though, since it may allow attackers to prevent the use of the system by a particular valid user. If the attacker impersonates the valid user, they may be able to prevent the user from accessing the server in question. The second solution is simply difficult to effectively institute -- and even when properly done, it does not provide a full solution. It simply makes the attack require more resources on the part of the attacker.
Architecture and Design: Ensure that protocols have specific limits of scale placed on them.
Implementation: Ensure that all failures in resource allocation place the system into a safe posture.

CWE-611: Improper Restriction of XML External Entity Reference

The product processes an XML document that can contain XML entities with URIs that resolve to documents outside of the intended sphere of control, causing the product to embed incorrect documents into its output.