CVE-2026-45491: Microsoft .NET improper link resolution in file access

CVE-2026-45491 · Severity: medium · CVSS 6.8 · Published 2026-06-09

A security flaw exists in the .NET component used for handling TAR archive files. An attacker could use a specially crafted archive to write files to unauthorized locations on a computer, potentially overwriting critical system or application files. This could lead to system instability or unauthorized changes to software configuration.

Technologies: Microsoft .NET Core Runtime, Microsoft.NetCore.App.Runtime.linux-x64 (NuGet), Microsoft.NetCore.App.Runtime.osx-arm64 (NuGet), Microsoft.NetCore.App.Runtime.win-x64 (NuGet). Vendors: Microsoft, NuGet.

Quick answers

Is CVE-2026-45491 exploited in the wild?
No. Junglewise Threat Intelligence has no report of CVE-2026-45491 being exploited in the wild.
How severe is CVE-2026-45491?
Medium severity, with a CVSS score of 6.8, published 9 June 2026.
Which products and versions are affected?
Microsoft .NET Core Runtime >= 8.0.0, <= 8.0.27; >= 9.0.0, <= 9.0.16; >= 10.0.0, <= 10.0.8; Microsoft.NetCore.App.Runtime.linux-x64 (NuGet) ECOSYSTEM:introduced=8.0.0,fixed=8.0.28; Microsoft.NetCore.App.Runtime.osx-arm64 (NuGet) ECOSYSTEM:introduced=8.0.0,fixed=8.0.28; Microsoft.NetCore.App.Runtime.win-x64 (NuGet) ECOSYSTEM:introduced=8.0.0,fixed=8.0.28.
Is there a fix for CVE-2026-45491?
Yes. Microsoft.NetCore.App.Runtime.linux-x64 (NuGet): upgrade to 8.0.28 or later; Microsoft.NetCore.App.Runtime.osx-arm64 (NuGet): upgrade to 8.0.28 or later; Microsoft.NetCore.App.Runtime.win-x64 (NuGet): upgrade to 8.0.28 or later. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.
How is CVE-2026-45491 attacked?
It is attacked with local access, in a software library.
Am I affected by CVE-2026-45491?
Check whether you run Microsoft .NET Core Runtime, Microsoft.NetCore.App.Runtime.linux-x64 (NuGet), Microsoft.NetCore.App.Runtime.osx-arm64 (NuGet) or one of the others listed at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

How to fix

  • Microsoft.NetCore.App.Runtime.linux-x64 (NuGet): upgrade to 8.0.28 or later
    dotnet add package Microsoft.NetCore.App.Runtime.linux-x64 --version 8.0.28
  • Microsoft.NetCore.App.Runtime.osx-arm64 (NuGet): upgrade to 8.0.28 or later
    dotnet add package Microsoft.NetCore.App.Runtime.osx-arm64 --version 8.0.28
  • Microsoft.NetCore.App.Runtime.win-x64 (NuGet): upgrade to 8.0.28 or later
    dotnet add package Microsoft.NetCore.App.Runtime.win-x64 --version 8.0.28

Technical details

A tampering vulnerability (CWE-59) exists in the System.Formats.Tar library within the TarFile.ExtractToDirectory method. The root cause is improper link resolution (symlink path traversal) during the extraction process. A local attacker can provide a malicious TAR archive containing symbolic links that, when extracted, allow the attacker to perform arbitrary file writes outside of the target extraction directory. This can result in the modification of sensitive files or application binaries. Microsoft has released patches for .NET 8, 9, and 10 to address this issue.

Affected products

  • Microsoft Microsoft.NETCore.App.Runtime >= 8.0.0, <= 8.0.27; >= 9.0.0, <= 9.0.16; >= 10.0.0, <= 10.0.8

Identifiers

  • CVE-2026-45491
  • GHSA-7q4v-2mr6-5gpx

Timeline

  • 2026-06-09: disclosed: Initial advisory publication
  • 2026-06-09: patched: Patched versions 8.0.28, 9.0.17, and 10.0.9 released
  • 2026-06-16: advisory: GitHub Advisory reviewed and updated

References

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