CVE-2026-39399 NuGet Gallery: Arbitrary Blob Overwrite via Nuspec Confusion and URI Fragment Truncation
Attackers can overwrite arbitrary storage blobs via crafted NuGet package metadata, potentially leading to remote code execution or content tampering.
- Exploited in the wild
- Not known
- Login needed
- Any signed-in user
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- None listed
What is CVE-2026-39399?
CVE-2026-39399 is a critical path traversal vulnerability in NuGetGallery, published on 14 Apr 2026. Any signed-in user can exploit it over the network, with no action from the victim.
Official description
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.
Which versions are affected by CVE-2026-39399?
How do I fix CVE-2026-39399?
No fix has been published for CVE-2026-39399 yet. Limit exposure of the affected software until one is available.
Upgrade, and resolve every user-supplied path against an allowed base folder before opening it. More about Path traversal.
Is CVE-2026-39399 being exploited?
There is no known exploitation of CVE-2026-39399 in the wild and no public exploit code.
Sources
Also known as GHSA-9r3h-v4hx-rhfr.