CVE-2023-43320 in Backup Server
Summary
by MITRE • 10/25/2023
An issue in Proxmox Server Solutions GmbH Proxmox VE v.5.4 thru v.8.0, Proxmox Backup Server v.1.1 thru v.3.0, and Proxmox Mail Gateway v.7.1 thru v.8.0 allows a remote authenticated attacker to escalate privileges via bypassing the two-factor authentication component.
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Analysis
by VulDB Data Team • 10/25/2023
The vulnerability CVE-2023-43320 represents a critical privilege escalation flaw affecting multiple Proxmox products including Proxmox VE, Proxmox Backup Server, and Proxmox Mail Gateway across specific version ranges. This security weakness stems from an insufficient bypass mechanism that allows authenticated attackers to circumvent the mandatory two-factor authentication process, thereby gaining elevated system privileges without proper verification. The flaw exists within the authentication framework of these enterprise-grade virtualization and backup solutions, which are widely deployed in enterprise environments for managing virtual machines, backups, and email services. The vulnerability affects systems where administrators have configured two-factor authentication as a security control, yet the implementation contains a logical flaw that permits privilege escalation.
The technical implementation of this vulnerability demonstrates a failure in the authentication flow where the system does not properly validate the completion of two-factor authentication before granting elevated privileges. Attackers who have already established valid credentials can exploit this weakness to bypass the second authentication factor, which typically involves time-based one-time passwords or hardware tokens. This flaw aligns with CWE-305 Authentication Bypass Through Multiple Implementations, where the system's authentication mechanism contains multiple entry points that can be exploited to circumvent security controls. The vulnerability essentially creates a backdoor path through the security architecture that should have prevented unauthorized privilege escalation, making it particularly dangerous in environments where administrative access to virtualization infrastructure is critical.
The operational impact of this vulnerability extends beyond simple privilege escalation, as it enables attackers to gain full administrative control over virtualized environments and backup systems. In Proxmox VE deployments, this could allow an attacker to manipulate virtual machines, access sensitive data, modify configurations, or even create new virtual environments. For Proxmox Backup Server environments, the implications include unauthorized access to backup data, potential data exfiltration, or manipulation of backup schedules and retention policies. The Proxmox Mail Gateway vulnerability could lead to email content manipulation, spam relay abuse, or complete compromise of email infrastructure. These attacks can be particularly devastating in enterprise environments where these systems manage critical infrastructure components, as they provide attackers with a persistent foothold that can be used for lateral movement and further compromise of the network. The vulnerability also violates fundamental security principles outlined in the MITRE ATT&CK framework under T1566 Credential Access and T1078 Valid Accounts, as it allows unauthorized privilege escalation through legitimate authentication mechanisms.
Organizations affected by this vulnerability should immediately implement mitigations including applying the latest security patches released by Proxmox, reviewing and strengthening authentication policies, and monitoring for unauthorized access attempts. System administrators should consider implementing additional security controls such as network segmentation, enhanced logging, and regular security audits to detect potential exploitation attempts. The vulnerability highlights the importance of proper authentication flow implementation and demonstrates how seemingly minor flaws in security architecture can have significant operational consequences. Organizations should also consider implementing zero-trust network principles and additional verification mechanisms to reduce the impact of such vulnerabilities in their environments. Regular security assessments and penetration testing should be conducted to identify similar weaknesses in authentication mechanisms across all enterprise systems.