What is the CVSS score of CVE-2026-21666?

CVE-2026-21666 has a CVSS 3.1 base score of 9.9 (Critical). CVSS vector: CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:H/I:H/A:H. EPSS exploitation probability: 0.4%.

Which versions of Veeam Backup Replication are affected by CVE-2026-21666?

A critical vulnerability in our Backup Server allows any authenticated domain user to execute arbitrary code remotely, potentially compromising our backup infrastructure and enabling data…

How to fix or mitigate CVE-2026-21666?

Within 24 hours: Isolate the Backup Server from the domain and restrict network access to authorized administrators only; audit backup logs for suspicious activity. Within 7 days: Implement network segmentation to limit domain user access to the Backup Server; disable non-essential authentication methods; deploy enhanced monitoring on backup server processes. Within 30 days: Establish a vendor communication plan to obtain a patch timeline; evaluate alternative backup solutions; conduct a full backup integrity assessment and security audit.

Veeam Backup Replication CVE-2026-21666

CRITICAL

Improper Access Control (CWE-284)

2026-03-12 support@hackerone.com

RCE Authentication Bypass Veeam Backup Replication

9.9

CVSS 3.1 · NVD

Severity by source

NVD PRIMARY

9.9 CRITICAL

AV:N/AC:L/PR:L/UI:N/S:C/C:H/I:H/A:H

Primary rating from NVD · only source for this CVE.

CVSS VectorNVD

CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:H/I:H/A:H

Attack Vector

Network

Attack Complexity

Low

Privileges Required

Low

User Interaction

None

Scope

Changed

Confidentiality

High

Integrity

High

Availability

High

Lifecycle Timeline

Analysis Generated

Mar 12, 2026 - 19:57 vuln.today

CVE Published

Mar 12, 2026 - 15:16 nvd

CRITICAL 9.9

DescriptionCVE.org

A vulnerability allowing an authenticated domain user to perform remote code execution (RCE) on the Backup Server.

AnalysisAI

Veeam Backup & Replication allows an authenticated domain user to achieve remote code execution on the Backup Server. With a scope change to CVSS 9.9, a compromised domain account can fully take over the backup infrastructure.

Technical ContextAI

An authenticated domain user can exploit improper access controls (CWE-284) to execute arbitrary code on the Veeam Backup Server. The scope change indicates the attacker breaks out of the Veeam application to compromise the underlying server OS. Since Veeam servers have privileged access to all protected infrastructure, this is a critical lateral movement vector.

RemediationAI

Apply Veeam security patches immediately. Isolate Veeam servers on dedicated management networks. Implement immutable backup copies. Monitor for anomalous domain user access to backup infrastructure.