CVE-2026-39399Network attack vector

Arbitrary blob overwrite via URI fragment truncation

Published Apr 14, 2026 · Updated Apr 14, 2026

Improper input validation in NuGet Gallery allows attackers to overwrite arbitrary blobs through crafted package metadata. The catalog backend trusts a package identifier from .nuspec metadata when resolving a storage URI, and an injected fragment truncates the blob path. The attacker must be able to submit a package; cross-package metadata injection can tamper with existing container content and lead to code execution.

CVSS severityUnavailable
Unscored
EPSS probability0.53%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Improper input validation in NuGet Gallery allows attackers to overwrite arbitrary blobs through crafted package metadata. The catalog backend trusts a package identifier from .nuspec metadata when resolving a storage URI, and an injected fragment truncates the blob path. The attacker must be able to submit a package; cross-package metadata injection can tamper with existing container content and lead to code execution.

The record

CVE
CVE-2026-39399
Published
Apr 14, 2026
Updated
Apr 14, 2026
Vendor
Microsoft
Product
NuGet Gallery
Classifications
T1565.001
Attack vector
network
Privileges
Unavailable

Timeline

How it unfolded

  1. Apr 14, 2026CVE publishedPublication date reported by the CVE source.
  2. Apr 14, 2026Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

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  1. Affected versionversion=< 0e80f87628349207cdcaf55358491f8a6f1ca276

What conditions does exploitation require?

Attack vectornetwork
Required privilegesUnavailable in this record.

What is affected?

Microsoft · NuGet Galleryversion=< 0e80f87628349207cdcaf55358491f8a6f1ca276

Published CVSS scores

No CVSS assessment is available in this record.

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

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No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
PrivilegesUnavailable
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

T1565.001Stored Data Manipulation

Public exploit references

No public exploit references are available in this record.

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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