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CVE-2026-39399

Critical Vulnerability: CVE-2026-39399

NuGet Gallery is a package repository that powers nuget.org. A security vulnerability exists in the NuGetGallery backend job’s handling of .nuspec files within NuGet packages. An attacker can supply a crafted nuspec file with malicious metadata, leading to cross package metadata injection that may result in remote code execution (RCE) and/or arbitrary blob writes due to insufficient input validation. The issue is exploitable via URI fragment injection using unsanitized package identifiers, allow

Tuesday, April 14, 2026Vulnios Threat Intelligence
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Executive Summary

NuGet Gallery is a package repository that powers nuget.org. A security vulnerability exists in the NuGetGallery backend job’s handling of .nuspec files within NuGet packages. An attacker can supply a crafted nuspec file with malicious metadata, leading to cross package metadata injection that may result in remote code execution (RCE) and/or arbitrary blob writes due to insufficient input validation. The issue is exploitable via URI fragment injection using unsanitized package identifiers, allowing an attacker to control the resolved blob path. This enables writes to arbitrary blobs within the storage container, not limited to .nupkg files, resulting in potential tampering of existing content. This issue has been patched in commit 0e80f87628349207cdcaf55358491f8a6f1ca276.

Why It Matters

CVE-2026-39399 is rated CRITICAL severity, requiring immediate attention from security teams.

CVSS Base Score: 9.6/10

🛡️What Defenders Should Check

  • Check if you are affected — Review your asset inventory for products listed in CVE-2026-39399.
  • Apply available patches — Visit vendor advisories for the latest security updates.
  • Monitor for exploitation — Check your SIEM/IDS logs for related indicators.

    • Use Vulnios to continuously monitor your exposure to CVE-2026-39399 and similar vulnerabilities.

    References & Sources

  • https://github.com/NuGet/NuGetGallery/commit/0e80f87628349207cdcaf55358491f8a6f1ca276
  • https://github.com/NuGet/NuGetGallery/security/advisories/GHSA-9r3h-v4hx-rhfr

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    Sources

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