CVE-2020-8103 in Antivirus Free
Summary
by MITRE
A vulnerability in the improper handling of symbolic links in Bitdefender Antivirus Free can allow an unprivileged user to substitute a quarantined file, and restore it to a privileged location. This issue affects Bitdefender Antivirus Free versions prior to 1.0.17.178.
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Analysis
by VulDB Data Team • 10/22/2020
The vulnerability identified as CVE-2020-8103 represents a critical privilege escalation flaw within Bitdefender Antivirus Free software that stems from improper handling of symbolic links during file quarantine operations. This weakness allows unprivileged users to exploit the antivirus system's file management processes and potentially gain elevated privileges by manipulating the quarantine mechanism. The issue specifically affects versions prior to 1.0.17.178, indicating that Bitdefender addressed this concern in their subsequent releases through code modifications and improved file handling protocols. The vulnerability manifests when the antivirus system processes symbolic links during quarantine operations, creating an opportunity for malicious actors to substitute quarantined files with malicious content.
The technical flaw involves a race condition and improper validation of symbolic link references within the Bitdefender quarantine subsystem. When the antivirus software encounters a file that requires quarantine, it creates a symbolic link to the original file location while moving the actual file to a secure quarantine directory. However, the implementation fails to properly verify the integrity and authenticity of these symbolic links, allowing an unprivileged user to create a malicious symbolic link that points to a privileged location. This creates a scenario where a quarantined file can be replaced with a malicious version that gets restored to a location with elevated privileges, effectively bypassing the security controls designed to isolate potentially malicious content.
The operational impact of this vulnerability extends beyond simple privilege escalation as it fundamentally undermines the core security principle of containment within antivirus systems. An attacker who gains access to a low-privilege account can exploit this flaw to restore malicious files to sensitive system locations such as system directories or configuration files, potentially leading to complete system compromise. The vulnerability enables attackers to circumvent the quarantine mechanism that is specifically designed to prevent malicious files from executing or accessing privileged resources. This represents a significant weakening of the antivirus's security posture and could allow for persistent threats, data exfiltration, or further system compromise through the restored malicious files.
Security professionals should consider this vulnerability in the context of the CWE-367 weakness category, which specifically addresses Time-of-Check to Time-of-Use (TOCTOU) race conditions that can lead to privilege escalation. The ATT&CK framework would categorize this as privilege escalation through exploitation of software vulnerabilities, potentially mapping to techniques such as T1068 for local privilege escalation and T1548 for abuse of elevation control mechanisms. Organizations should implement immediate mitigations including patching to the latest Bitdefender Antivirus Free version, monitoring for unauthorized symbolic link creation in system directories, and implementing additional access controls to prevent unprivileged users from manipulating critical system locations. The vulnerability also highlights the importance of proper input validation and secure file handling practices in security software, particularly when dealing with user-supplied data that could be used to manipulate system state through symbolic link manipulation.