CVE-2021-43040 in Unitrends Backup Appliance
Summary
by MITRE • 12/06/2021
An issue was discovered in Kaseya Unitrends Backup Appliance before 10.5.5. The privileged vaultServer could be leveraged to create arbitrary writable files, leading to privilege escalation.
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Analysis
by VulDB Data Team • 12/09/2021
The vulnerability identified as CVE-2021-43040 represents a critical privilege escalation flaw within the Kaseya Unitrends Backup Appliance software ecosystem. This vulnerability specifically affects versions prior to 10.5.5 and stems from improper access controls within the privileged vaultServer component. The flaw allows authenticated attackers with limited privileges to exploit a weakness in the file system permissions model, enabling them to create arbitrary writable files that can be used to escalate their privileges within the system. This represents a fundamental breakdown in the principle of least privilege that is essential for maintaining system integrity and security boundaries.
The technical implementation of this vulnerability involves a misconfiguration or code flaw within the vaultServer process that handles sensitive backup operations. When legitimate users interact with the backup appliance, the system fails to properly validate file creation requests against the appropriate access control lists. This weakness creates an opportunity for attackers to manipulate file system operations and establish writable file permissions that would normally be restricted to privileged system components. The vulnerability operates at the operating system level where file permissions and access controls should prevent unauthorized modification of critical system files, yet the flaw allows bypassing these security mechanisms through legitimate system interfaces.
From an operational impact perspective, this vulnerability presents a severe risk to organizations relying on Kaseya Unitrends Backup Appliances for their data protection infrastructure. The ability to create arbitrary writable files means that an attacker could potentially modify system binaries, configuration files, or create backdoor mechanisms that persist across system restarts. This privilege escalation capability allows attackers to gain root or administrator-level access to the backup appliance, which serves as a critical component in enterprise data protection strategies. The compromised appliance could then be used to access, modify, or exfiltrate backup data, potentially leading to complete data loss or unauthorized access to sensitive organizational information.
Organizations should prioritize immediate remediation of this vulnerability by upgrading to Kaseya Unitrends Backup Appliance version 10.5.5 or later, which contains the necessary patches to address the privilege escalation flaw. Security teams should implement network segmentation to limit access to backup appliances and ensure that only authorized personnel can interact with these systems. Additionally, monitoring should be implemented to detect unusual file creation patterns or permission changes that might indicate exploitation attempts. The vulnerability aligns with CWE-276, which describes improper file permissions, and represents a clear violation of the ATT&CK technique T1068, which covers exploit for privilege escalation. Organizations should also consider implementing additional security controls such as mandatory access controls, file integrity monitoring, and regular security assessments to prevent similar vulnerabilities from being exploited in their environments.