CVE-2026-26171

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…

.NET is a managed-software framework. It implements a subset of the .NET framework APIs and several new APIs, and it includes a CLR implementation.

New versions of .NET that address a security vulnerability are now available. The updated versions are .NET SDK 10.0.106 and .NET Runtime 10.0.6.Security Fix(es):

• dotnet: .NET: Security Bypass and Denial of Service Vulnerability (CVE-2026-26171)

• dotnet: .NET: Denial of Service via stack overflow (CVE-2026-32203)

• dotnet: .NET: Denial of Service via Infinite Recursion in XmlDecryptionTransform (CVE-2026-33116)

• dotnet: Dotnet: SMTP Command Injection and Header Injection via MailAddress parsing flaw (CVE-2026-32178)

For more details about the security issue(s), including the impact, a CVSS score, acknowledgments, and other related information, refer to the CVE page(s) listed in the References section.

.NET is a managed-software framework. It implements a subset of the .NET framework APIs and several new APIs, and it includes a CLR implementation.

New versions of .NET that address a security vulnerability are now available. The updated versions are .NET SDK SDK_VERSION and .NET Runtime RUNTIME_VERSION.Security Fix(es):

• dotnet: .NET: Security Bypass and Denial of Service Vulnerability (CVE-2026-26171)

• dotnet: .NET: Denial of Service via stack overflow (CVE-2026-32203)

• dotnet: .NET: Denial of Service via Infinite Recursion in XmlDecryptionTransform (CVE-2026-33116)

• dotnet: Dotnet: SMTP Command Injection and Header Injection via MailAddress parsing flaw (CVE-2026-32178)

For more details about the security issue(s), including the impact, a CVSS score, acknowledgments, and other related information, refer to the CVE page(s) listed in the References section.

.NET is a managed-software framework. It implements a subset of the .NET framework APIs and several new APIs, and it includes a CLR implementation.

New versions of .NET that address a security vulnerability are now available. The updated versions are .NET SDK 8.0.126 and .NET Runtime 8.0.26.Security Fix(es):

• dotnet: .NET: Security Bypass and Denial of Service Vulnerability (CVE-2026-26171)

• dotnet: .NET: Denial of Service via stack overflow (CVE-2026-32203)

• dotnet: .NET: Denial of Service via Infinite Recursion in XmlDecryptionTransform (CVE-2026-33116)

• dotnet: Dotnet: SMTP Command Injection and Header Injection via MailAddress parsing flaw (CVE-2026-32178)

For more details about the security issue(s), including the impact, a CVSS score, acknowledgments, and other related information, refer to the CVE page(s) listed in the References section.

.NET is a managed-software framework. It implements a subset of the .NET framework APIs and several new APIs, and it includes a CLR implementation.

New versions of .NET that address a security vulnerability are now available. The updated versions are .NET SDK 8.0.126 and .NET Runtime 8.0.26.Security Fix(es):

• dotnet: .NET: Security Bypass and Denial of Service Vulnerability (CVE-2026-26171)

• dotnet: .NET: Denial of Service via stack overflow (CVE-2026-32203)

• dotnet: .NET: Denial of Service via Infinite Recursion in XmlDecryptionTransform (CVE-2026-33116)

• dotnet: Dotnet: SMTP Command Injection and Header Injection via MailAddress parsing flaw (CVE-2026-32178)

For more details about the security issue(s), including the impact, a CVSS score, acknowledgments, and other related information, refer to the CVE page(s) listed in the References section.

.NET is a managed-software framework. It implements a subset of the .NET framework APIs and several new APIs, and it includes a CLR implementation.

New versions of .NET that address a security vulnerability are now available. The updated versions are .NET SDK 10.0.106 and .NET Runtime 10.0.6.Security Fix(es):

• dotnet: .NET: Security Bypass and Denial of Service Vulnerability (CVE-2026-26171)

• dotnet: .NET: Denial of Service via stack overflow (CVE-2026-32203)

• dotnet: .NET: Denial of Service via Infinite Recursion in XmlDecryptionTransform (CVE-2026-33116)

• dotnet: Dotnet: SMTP Command Injection and Header Injection via MailAddress parsing flaw (CVE-2026-32178)

For more details about the security issue(s), including the impact, a CVSS score, acknowledgments, and other related information, refer to the CVE page(s) listed in the References section.

.NET is a managed-software framework. It implements a subset of the .NET framework APIs and several new APIs, and it includes a CLR implementation.

New versions of .NET that address a security vulnerability are now available. The updated versions are .NET SDK 9.0.116 and .NET Runtime 9.0.15.Security Fix(es):

• dotnet: .NET: Security Bypass and Denial of Service Vulnerability (CVE-2026-26171)

• dotnet: .NET: Denial of Service via stack overflow (CVE-2026-32203)

• dotnet: .NET: Denial of Service via Infinite Recursion in XmlDecryptionTransform (CVE-2026-33116)

• dotnet: Dotnet: SMTP Command Injection and Header Injection via MailAddress parsing flaw (CVE-2026-32178)

For more details about the security issue(s), including the impact, a CVSS score, acknowledgments, and other related information, refer to the CVE page(s) listed in the References section.

.NET is a managed-software framework. It implements a subset of the .NET framework APIs and several new APIs, and it includes a CLR implementation.

New versions of .NET that address a security vulnerability are now available. The updated versions are .NET SDK 10.0.106 and .NET Runtime 10.0.6.Security Fix(es):

• dotnet: .NET: Security Bypass and Denial of Service Vulnerability (CVE-2026-26171)

• dotnet: .NET: Denial of Service via stack overflow (CVE-2026-32203)

• dotnet: .NET: Denial of Service via Infinite Recursion in XmlDecryptionTransform (CVE-2026-33116)

• dotnet: Dotnet: SMTP Command Injection and Header Injection via MailAddress parsing flaw (CVE-2026-32178)

For more details about the security issue(s), including the impact, a CVSS score, acknowledgments, and other related information, refer to the CVE page(s) listed in the References section.

.NET is a managed-software framework. It implements a subset of the .NET framework APIs and several new APIs, and it includes a CLR implementation.

New versions of .NET that address a security vulnerability are now available. The updated versions are .NET SDK 9.0.116 and .NET Runtime 9.0.15.Security Fix(es):

• dotnet: .NET: Security Bypass and Denial of Service Vulnerability (CVE-2026-26171)

• dotnet: .NET: Denial of Service via stack overflow (CVE-2026-32203)

• dotnet: .NET: Denial of Service via Infinite Recursion in XmlDecryptionTransform (CVE-2026-33116)

• dotnet: Dotnet: SMTP Command Injection and Header Injection via MailAddress parsing flaw (CVE-2026-32178)

For more details about the security issue(s), including the impact, a CVSS score, acknowledgments, and other related information, refer to the CVE page(s) listed in the References section.

.NET is a managed-software framework. It implements a subset of the .NET framework APIs and several new APIs, and it includes a CLR implementation.

New versions of .NET that address a security vulnerability are now available. The updated versions are .NET SDK 9.0.116 and .NET Runtime 9.0.15.Security Fix(es):

• dotnet: .NET: Security Bypass and Denial of Service Vulnerability (CVE-2026-26171)

• dotnet: .NET: Denial of Service via stack overflow (CVE-2026-32203)

• dotnet: .NET: Denial of Service via Infinite Recursion in XmlDecryptionTransform (CVE-2026-33116)

• dotnet: Dotnet: SMTP Command Injection and Header Injection via MailAddress parsing flaw (CVE-2026-32178)

For more details about the security issue(s), including the impact, a CVSS score, acknowledgments, and other related information, refer to the CVE page(s) listed in the References section.

Root has patched CVE-2026-26171 in the System.Security.Cryptography.Xml package for Root:NuGet. Multiple fixed versions available.

Uncontrolled resource consumption in .NET allows an unauthorized attacker to deny service over a network.

.NET is a managed-software framework. It implements a subset of the .NET framework APIs and several new APIs, and it includes a CLR implementation.

New versions of .NET that address a security vulnerability are now available. The updated versions are .NET SDK SDK_VERSION and .NET Runtime RUNTIME_VERSION.Security Fix(es):

• dotnet: .NET: Security Bypass and Denial of Service Vulnerability (CVE-2026-26171)
• dotnet: .NET: Denial of Service via stack overflow (CVE-2026-32203)
• dotnet: .NET: Denial of Service via Infinite Recursion in XmlDecryptionTransform (CVE-2026-33116)
• dotnet: Dotnet: SMTP Command Injection and Header Injection via MailAddress parsing flaw (CVE-2026-32178)

For more details about the security issue(s), including the impact, a CVSS score, acknowledgments, and other related information, refer to the CVE page(s) listed in the References section.

.NET is a managed-software framework. It implements a subset of the .NET framework APIs and several new APIs, and it includes a CLR implementation.

New versions of .NET that address a security vulnerability are now available. The updated versions are .NET SDK 8.0.126 and .NET Runtime 8.0.26.Security Fix(es):

• dotnet: .NET: Security Bypass and Denial of Service Vulnerability (CVE-2026-26171)
• dotnet: .NET: Denial of Service via stack overflow (CVE-2026-32203)
• dotnet: .NET: Denial of Service via Infinite Recursion in XmlDecryptionTransform (CVE-2026-33116)
• dotnet: Dotnet: SMTP Command Injection and Header Injection via MailAddress parsing flaw (CVE-2026-32178)

For more details about the security issue(s), including the impact, a CVSS score, acknowledgments, and other related information, refer to the CVE page(s) listed in the References section.

.NET is a managed-software framework. It implements a subset of the .NET framework APIs and several new APIs, and it includes a CLR implementation.

New versions of .NET that address a security vulnerability are now available. The updated versions are .NET SDK 8.0.126 and .NET Runtime 8.0.26.Security Fix(es):

• dotnet: .NET: Security Bypass and Denial of Service Vulnerability (CVE-2026-26171)
• dotnet: .NET: Denial of Service via stack overflow (CVE-2026-32203)
• dotnet: .NET: Denial of Service via Infinite Recursion in XmlDecryptionTransform (CVE-2026-33116)
• dotnet: Dotnet: SMTP Command Injection and Header Injection via MailAddress parsing flaw (CVE-2026-32178)

For more details about the security issue(s), including the impact, a CVSS score, acknowledgments, and other related information, refer to the CVE page(s) listed in the References section.

.NET is a managed-software framework. It implements a subset of the .NET framework APIs and several new APIs, and it includes a CLR implementation.

New versions of .NET that address a security vulnerability are now available. The updated versions are .NET SDK 9.0.116 and .NET Runtime 9.0.15.Security Fix(es):

• dotnet: .NET: Security Bypass and Denial of Service Vulnerability (CVE-2026-26171)
• dotnet: .NET: Denial of Service via stack overflow (CVE-2026-32203)
• dotnet: .NET: Denial of Service via Infinite Recursion in XmlDecryptionTransform (CVE-2026-33116)
• dotnet: Dotnet: SMTP Command Injection and Header Injection via MailAddress parsing flaw (CVE-2026-32178)

For more details about the security issue(s), including the impact, a CVSS score, acknowledgments, and other related information, refer to the CVE page(s) listed in the References section.

.NET is a managed-software framework. It implements a subset of the .NET framework APIs and several new APIs, and it includes a CLR implementation.

New versions of .NET that address a security vulnerability are now available. The updated versions are .NET SDK 10.0.106 and .NET Runtime 10.0.6.Security Fix(es):

• dotnet: .NET: Security Bypass and Denial of Service Vulnerability (CVE-2026-26171)
• dotnet: .NET: Denial of Service via stack overflow (CVE-2026-32203)
• dotnet: .NET: Denial of Service via Infinite Recursion in XmlDecryptionTransform (CVE-2026-33116)
• dotnet: Dotnet: SMTP Command Injection and Header Injection via MailAddress parsing flaw (CVE-2026-32178)

For more details about the security issue(s), including the impact, a CVSS score, acknowledgments, and other related information, refer to the CVE page(s) listed in the References section.

.NET is a managed-software framework. It implements a subset of the .NET framework APIs and several new APIs, and it includes a CLR implementation.

New versions of .NET that address a security vulnerability are now available. The updated versions are .NET SDK 9.0.116 and .NET Runtime 9.0.15.Security Fix(es):

• dotnet: .NET: Security Bypass and Denial of Service Vulnerability (CVE-2026-26171)
• dotnet: .NET: Denial of Service via stack overflow (CVE-2026-32203)
• dotnet: .NET: Denial of Service via Infinite Recursion in XmlDecryptionTransform (CVE-2026-33116)
• dotnet: Dotnet: SMTP Command Injection and Header Injection via MailAddress parsing flaw (CVE-2026-32178)

For more details about the security issue(s), including the impact, a CVSS score, acknowledgments, and other related information, refer to the CVE page(s) listed in the References section.

Uncontrolled resource consumption in .NET allows an unauthorized attacker to deny service over a network.

Uncontrolled resource consumption in .NET allows an unauthorized attacker to deny service over a network.

Uncontrolled resource consumption in .NET allows an unauthorized attacker to deny service over a network.

Ludvig Pedersen discovered that the System.Security.Cryptography.Xml library in .NET incorrectly handled certain XML inputs. An attacker could possibly use this issue to consume excessive resources, resulting in a denial of service. (CVE-2026-33116, CVE-2026-26171)

Ludvig Pedersen and Kevin Jones discovered that the System.Security.Cryptography.Xml library in .NET incorrectly handled certain XML inputs. An attacker could possibly use this issue to cause .NET to crash, resulting in a denial of service. (CVE-2026-32203)

Ludvig Pedersen discovered that the System.Net.Mail component in .NET incorrectly handled certain inputs. An attacker could possibly use this issue to perform a network spoofing attack. (CVE-2026-32178)

Ludvig Pedersen discovered that the System.Security.Cryptography.Xml library in .NET incorrectly handled certain XML inputs. An attacker could possibly use this issue to consume excessive resources, resulting in a denial of service. (CVE-2026-33116, CVE-2026-26171)

Ludvig Pedersen and Kevin Jones discovered that the System.Security.Cryptography.Xml library in .NET incorrectly handled certain XML inputs. An attacker could possibly use this issue to cause .NET to crash, resulting in a denial of service. (CVE-2026-32203)

Ludvig Pedersen discovered that the System.Net.Mail component in .NET incorrectly handled certain inputs. An attacker could possibly use this issue to perform a network spoofing attack. (CVE-2026-32178)

It was discovered that the Microsoft.AspNetCore.DataProtection library in .NET did not properly verify cryptographic signatures under certain conditions. A remote attacker could possibly use this issue to elevate privileges. (CVE-2026-40372)