What is CVE-2026-21666?
A vulnerability allowing an authenticated domain user to perform remote code execution (RCE) on the Backup Server.
The record classifies CVE-2026-21666 under weakness class CWE-284. Its CVSS v3 base vector states that the flaw is reachable remotely over the network, needs low-privilege credentials, needs no user interaction, and has high impact on confidentiality, integrity, availability. 1 affected-product entry is recorded, across 1 vendor, listed below. The identifier was first published 234 days ago.
Severity and exploitation probability
- CVSS v3.1 base score
- 9.9 — CRITICAL
CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:H/I:H/A:H - EPSS (FIRST)
- 1.1% probability of exploitation in the next 30 days, higher than 65.8% of all scored CVEs
- CISA KEV
- Not listed in the CISA Known Exploited Vulnerabilities catalog
- Threadlinqs priority
- 7.6/10 — a Threadlinqs composite of the CVSS base score, the EPSS percentile and public exploit availability
- Published
- 2026-03-12, last modified 2026-03-13
Is CVE-2026-21666 being exploited?
It currently carries a trending score of 26 in the Threadlinqs vulnerability feed.
Affected products and versions
- Veeam: Backup & Replication
How to fix CVE-2026-21666
The record marks a vendor fix as available for CVE-2026-21666. Vendor advisory: https://www.veeam.com/kb4830. Apply the vendor fix referenced above to every affected product listed in this record, then confirm the running version against the vendor advisory.
Threat activity tracking CVE-2026-21666
2 tracked threats in the Threadlinqs corpus reference CVE-2026-21666, either in the campaign’s CVE list or as an indicator on the campaign record.
- Ransomware Targeting of Backup Infrastructure: Akira/Fog/Frag Exploiting Veeam CVE-2024-40711, Plus CVE-2025-23120 and March 2026 Backup & Replication Flaws (CVE-2026-21666/21667/21708) — CRITICAL · 2026-10-31
- Veeam Backup & Replication 8 Critical Vulnerabilities — Domain User to Backup Server RCE (CVE-2026-21666, CVE-2026-21667, CVE-2026-21669, CVE-2026-21708) — CRITICAL · 2026-03-15
Sources
Enriched from CVE.org, NVD, FIRST EPSS, GitHub Security Advisories. Last verified by Threadlinqs on . This product uses the NVD API but is not endorsed or certified by the NVD.