Microsoft Security Advisory CVE-2026-45491 – .NET Tampering Vulnerability
Date: 2026-06
Affected: nuget/Microsoft.NETCore.App.Runtime.osx-arm64, nuget/Microsoft.NETCore.App.Runtime.osx-arm64, nuget/Microsoft.NETCore.App.Runtime.osx-arm64
Attack vector: path-traversal
Category: vulnerability-disclosure
Severity: Medium
CVE: CVE-2026-45491
CWE: CWE-59
CVSS: 6.8 (CVSS:3.1/AV:L/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:L)

## Executive Summary Microsoft is releasing this security advisory to provide information about a vulnerability in System.Formats.Tar. This advisory also provides guidance on what developers can do to update their applications to remove this vulnerability. A tampering vulnerability exists in the `TarFile.ExtractToDirectory` method where a symlink path traversal enables an attacker to perform arbitrary file writes outside the intended extraction directory. ## Announcement Announcement for this issue can be found at https://github.com/dotnet/announcements/issues/404 ## Affected Platforms - **Platforms:** All - **Architectures:** All ## Affected Packages The vulnerability affects any Microsoft .NET project if it uses any of affected package versions listed below ### .NET 10 Package name | Affected version | Patched version ------------ | ---------------- | ------------------------- [Microsoft.NETCore.App.Runtime](https://www.nuget.org/packages/Microsoft.NETCore.App.Runtime) | >= 10.0.0, <= 10.0.8 | 10.0.9 ### .NET 9 Package name | Affected version | Patched version ------------ | ---------------- | ------------------------- [Microsoft.NETCore.App.Runtime](https://www.nuget.org/packages/Microsoft.NETCore.App.Runtime) | >= 9.0.0, <= 9.0.16 | 9.0.17 ### .NET 8 Package name | Affected version | Patched version ------------ | ---------------- | ------------------------- [Microsoft.NETCore.App.Runtime](https://www.nuget.org/packages/Microsoft.NETCore.App.Runtime) | >= 8.0.0,


Mitigations:

Architectural layers (MAESTRO):