Zoom macOS Client Privilege Escalation Vulnerability

The Zoom macOS client, specifically version 4.6.8 (19178.0323) and earlier, contains a local privilege escalation vulnerability. This vulnerability stems from the insecure use of the deprecated AuthorizationExecuteWithPrivileges API. The Zoom installer copies a bash script named runwithroot to a user-writable temporary directory. A local, unprivileged attacker can subvert this script before it is executed as root, thereby escalating their privileges. The vulnerability requires a local foothold on the macOS system and relies on the installer or updater being executed. While Zoom has faced other security and privacy concerns, this particular flaw allows for a complete takeover of the system by a local attacker. This privilege escalation vulnerability poses a significant risk, particularly in environments where multiple users share a single macOS system or where malware may already have a limited foothold. Zoom patched this in version 4.6.9 (19273.0402).

Attack Chain

1. Attacker gains initial access to the macOS system via malware or other means.
2. The Zoom installer package (Zoom.pkg) is executed, either by the user or automatically through an update.
3. The macOS Installer copies the runwithroot script to a user-writable temporary directory, such as /private/var/folders/v5/s530008n11dbm2n2pgzxkk700000gp/T/com.apple.install.v43Mcm4r/.
4. The attacker identifies the temporary directory and modifies the runwithroot script with malicious commands.
5. The installer invokes the AuthorizationExecuteWithPrivileges API, prompting the user for administrator credentials if they are not already an administrator.
6. The system executes /usr/libexec/security_authtrampoline with the runwithroot script as an argument.
7. The runwithroot script, now containing malicious commands, executes with root privileges.
8. The attacker achieves root-level access on the system, allowing them to perform any action they desire, such as installing malware, stealing data, or compromising other users.

Impact

Successful exploitation of this vulnerability allows a local attacker to gain complete control over the affected macOS system. The attacker can install persistent backdoors, steal sensitive data, or compromise other user accounts on the system. While the report does not specify the number of victims, the widespread use of Zoom makes this a high-impact vulnerability. Sectors targeted could include any organization using Zoom on macOS, potentially leading to significant data breaches or system compromise.

Recommendation

• Upgrade Zoom to version 4.6.9 (19273.0402) or later to patch the privilege escalation vulnerability.
• Deploy the Sigma rule Detect Modification of Zoom runwithroot Script to detect attempts to modify the vulnerable script.
• Monitor for the execution of security_authtrampoline with arguments pointing to user-writable directories, as indicated in the analysis of the AuthorizationExecuteWithPrivileges API usage.
• Enable process monitoring to detect the execution of scripts or binaries from temporary directories, which can indicate exploitation attempts.
• Consider disabling or restricting the use of the AuthorizationExecuteWithPrivileges API where possible, as recommended by Apple.