Affects widely-used NuGetGallery/nuget.org; RCE and blob writes threaten software supply chain.
CVE-2026-39399
Remote code execution and arbitrary blob writes via crafted nuspec in NuGetGallery
Is CVE-2026-39399 being exploited?
Not confirmed. CVE-2026-39399 does not appear in CISA's Known Exploited Vulnerabilities catalog, which records only exploitation that has been observed and reported publicly. That is evidence of absence of a report, not evidence the flaw is unattacked. EPSS currently estimates a 0.53% probability of exploitation in the next 30 days.
How severe is CVE-2026-39399?
CVE-2026-39399 is rated Critical with a CVSS score of 9.6. Severity describes how bad exploitation would be, not how likely it is: pair it with exploitation evidence before deciding what to patch first.
Is there a patch for CVE-2026-39399?
Yes. A fix has been recorded for CVE-2026-39399. The vendor advisory is the authority on the exact fixed version — apply it from there rather than from a summary.
What does CVE-2026-39399 affect?
CVE-2026-39399 affects NuGetGallery backend, nuget.org services. Confirm the exact affected versions against the vendor advisory before deciding you are exposed.
What should I do about CVE-2026-39399?
Apply the published patch; validate nuspec handling; monitor for abuse
Exploitation status reflects CISA's KEV catalog as we last synced it. Check the catalog directly.
RCE and arbitrary blob writes via unsanitized nuspec metadata and URI fragment injection
Patch when possible
- affected< 0e80f87628349207cdcaf55358491f8a6f1ca276
As published in the CVE Program record. A version outside these ranges is not a statement that it is unaffected — vendors sometimes understate a range, and distribution-backported builds carry upstream numbers that do not reflect what was patched into them.