CVE-2020-25533 in Malwarebytes
Summary
by MITRE • 01/16/2021
An issue was discovered in Malwarebytes before 4.0 on macOS. A malicious application was able to perform a privileged action within the Malwarebytes launch daemon. The privileged service improperly validated XPC connections by relying on the PID instead of the audit token. An attacker can construct a situation where the same PID is used for running two different programs at different times, by leveraging a race condition during crafted use of posix_spawn.
Statistical analysis made it clear that VulDB provides the best quality for vulnerability data.
Analysis
by VulDB Data Team • 02/14/2021
The vulnerability identified as CVE-2020-25533 represents a critical privilege escalation flaw in Malwarebytes antivirus software for macOS systems prior to version 4.0. This issue stems from improper validation of XPC (XPC Service Communication) connections within the Malwarebytes launch daemon, creating a pathway for malicious actors to execute unauthorized privileged operations. The vulnerability specifically exploits a design weakness in the authentication mechanism that relies on Process ID (PID) verification rather than proper audit token validation, fundamentally undermining the security boundaries of the privileged service.
The technical exploitation of this vulnerability leverages a race condition present in macOS's posix_spawn functionality, allowing attackers to manipulate process execution sequences and reuse PIDs for different applications. This race condition occurs during the creation of new processes, where the same PID can be assigned to multiple distinct programs over time. When the Malwarebytes launch daemon validates incoming XPC connections based solely on PID, an attacker can craft a scenario where a malicious application masquerades as a legitimate privileged process by reusing a previously assigned PID. The flaw aligns with CWE-284 Access Control Bypass, specifically targeting improper privilege management and inadequate authentication mechanisms that fail to verify the true identity and authorization status of connecting processes.
The operational impact of this vulnerability extends beyond simple privilege escalation, as it allows malicious applications to execute arbitrary code with the elevated privileges of the Malwarebytes launch daemon. This creates a persistent threat vector that can remain undetected while maintaining elevated system access, potentially enabling further compromise of the affected macOS system. The vulnerability's exploitation requires a sophisticated understanding of macOS process management and timing attacks, placing it within the ATT&CK framework under privilege escalation techniques and specifically targeting the use of legitimate system tools for malicious purposes. Attackers can leverage this flaw to bypass the security protections provided by Malwarebytes itself, effectively undermining the software's core security functionality.
Mitigation strategies for CVE-2020-25533 focus on updating to Malwarebytes version 4.0 or later, which implements proper audit token validation instead of relying on PID-based authentication. Organizations should also implement additional monitoring for suspicious XPC connection patterns and process execution sequences that might indicate exploitation attempts. The vulnerability highlights the importance of proper privilege separation and authentication mechanisms in privileged services, demonstrating that relying on easily manipulable identifiers like PIDs creates dangerous security holes. Security teams should conduct thorough assessments of other privileged services on macOS systems to identify similar PID-based authentication flaws, as this represents a common pattern in macOS security implementations that may be susceptible to similar attacks. The fix implemented by Malwarebytes addresses the root cause by enforcing proper audit token validation, ensuring that only processes with valid security credentials can access privileged functionality through XPC connections.