Microsoft Security Advisory CVE-2026-26171 – .NET Denial of Service Vulnerability
Date: 2026-04
Affected: nuget/System.Security.Cryptography.Xml, nuget/System.Security.Cryptography.Xml, nuget/System.Security.Cryptography.Xml
Attack vector: dos
Category: vulnerability-disclosure
Severity: High
CVE: CVE-2026-26171
CWE: CWE-400
CWE-611
CVSS: 7.5 (CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H)

## 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](https://www.nuget.org/packages/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.Cr


Mitigations:

Architectural layers (MAESTRO):