NuGet Gallery: Arbitrary Blob Overwrite via Nuspec Confusion and URI Fragment Truncation

published 2026-04-14 6 mo ago modified 2026-07-24 3 mo ago also EUVD-2026-22805

cvss: 9.6; version 3.1, CNA
cisa kev: Not listed; not in CISA's catalog
epss: 0.5%; EPSS 0.5% chance of exploitation in 30 days, percentile 44%
public exploits: 0; none known

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.

Patch / fix

links 1

github.com/NuGet/NuGetGallery@0e80f87 commit

CISA SSVC

Exploitation: none
Automatable: no
Technical impact: partial
Assessed: 6 mo ago (2026-04-15)

Exploit prediction

0.53% chance of exploitation in the next 30 days, higher than 44% of all scored CVEs (FIRST EPSS, 2026-11-08).

CVSS scores

assigned by	version	score	vector
CNA	3.1	9.6	CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:N/I:H/A:H

Affected products

NuGet NuGetGallery

Classification

Weakness

CWE-20 Improper Input Validation
CWE-22 Improper Limitation of a Pathname to a Restricted Directory

References

Sources

CVE List CVE-2026-39399
NVD CVE-2026-39399

Fencer Vulns keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.

Summary