CVE-2021-43771 in Antivirus 2021
Summary
by MITRE • 11/30/2021
Trend Micro Antivirus for Mac 2021 v11 (Consumer) is vulnerable to an improper access control privilege escalation vulnerability that could allow an attacker to establish a connection that could lead to full local privilege escalation within the application. Please note that an attacker must first obtain the ability to execute low-privileged code on the target system in order to exploit this vulnerability.
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Analysis
by VulDB Data Team • 12/04/2021
The vulnerability identified as CVE-2021-43771 affects Trend Micro Antivirus for Mac 2021 version 11 consumer edition, representing a critical improper access control flaw that enables privilege escalation attacks. This vulnerability resides within the macOS antivirus software's permission handling mechanisms, specifically targeting how the application manages elevated privileges during execution. The flaw manifests when the antivirus software fails to properly validate or restrict access controls for certain internal processes or system components, creating a potential pathway for malicious actors to escalate their privileges from standard user level to full administrative access. The vulnerability's exploitation requires an initial foothold through the execution of low-privileged code on the target system, making it a post-compromise privilege escalation vector rather than an initial access vulnerability. This categorization aligns with CWE-284 which defines improper access control as a weakness where insufficient access control mechanisms allow unauthorized users to access protected resources or perform unauthorized operations. The attack surface is particularly concerning given that antivirus software typically runs with elevated privileges to perform system-level operations, making any access control flaw within such applications especially dangerous.
The technical implementation of this vulnerability stems from inadequate privilege management within the Trend Micro antivirus application's architecture. When the software executes certain operations that require elevated permissions, the access control validation mechanisms fail to properly enforce the principle of least privilege. This allows an attacker who has already compromised a low-privileged process to manipulate the application's behavior and gain access to higher-privileged operations. The flaw likely involves improper validation of process ownership, file permissions, or inter-process communication channels that the antivirus application uses to perform its security functions. Attackers can exploit this by establishing connections or manipulating system calls that should normally be restricted to privileged processes, effectively bypassing the application's intended security boundaries. The vulnerability's impact is amplified by the fact that antivirus software often requires broad system access to perform its core functions, creating a larger attack surface that can be exploited through privilege escalation techniques. This type of vulnerability is particularly dangerous because it can be leveraged to bypass other security controls that rely on the assumption that the antivirus application is running with appropriate privilege levels.
The operational impact of CVE-2021-43771 extends beyond simple privilege escalation, as it creates a persistent backdoor for attackers to maintain elevated access within the compromised system. Once successfully exploited, an attacker can gain complete control over the affected Mac system, potentially leading to data exfiltration, system compromise, or further lateral movement within network environments. The vulnerability's requirement for initial low-privileged code execution means that attackers would typically need to achieve initial access through other vectors such as phishing attacks, malicious software downloads, or exploitation of other system vulnerabilities before attempting to leverage this privilege escalation flaw. This makes the attack chain more complex but also more realistic given that initial access is often achieved through social engineering or other common attack vectors. The vulnerability's presence in antivirus software creates a particularly concerning scenario where the system's primary security defense mechanism becomes a potential attack vector. From an operational security perspective, this vulnerability undermines the fundamental trust model that users place in antivirus software to protect their systems, as the software itself becomes a potential entry point for attackers.
Mitigation strategies for CVE-2021-43771 should focus on both immediate remediation and long-term architectural improvements. The most effective immediate solution is to update to the latest version of Trend Micro Antivirus for Mac that contains patches addressing this specific access control flaw. System administrators should also implement additional monitoring for suspicious process behavior, particularly around antivirus-related processes that may attempt to establish unexpected connections or access restricted system resources. Network-based detection measures can help identify potential exploitation attempts by monitoring for unusual outbound connections or system calls that would indicate privilege escalation activity. The vulnerability's characteristics make it suitable for detection through behavioral analysis and anomaly detection systems that monitor process privileges and access patterns. Organizations should also consider implementing application whitelisting policies that restrict which processes can execute with elevated privileges, reducing the potential impact of such privilege escalation flaws. From a broader security perspective, this vulnerability highlights the importance of proper access control implementation in security software, particularly in applications that operate with elevated privileges. The flaw demonstrates why security controls must be designed with defense in depth principles, ensuring that even if one layer is compromised, other controls can prevent or detect unauthorized access attempts. This vulnerability also underscores the necessity of regular security assessments and penetration testing of security software to identify access control flaws before they can be exploited by malicious actors. The ATT&CK framework categorizes this type of vulnerability under privilege escalation techniques, specifically targeting the use of software vulnerabilities to gain elevated privileges, making it a key consideration for security teams implementing threat hunting and incident response procedures.