CVE-2024-23460

Executive Summary

CVE-2024-23460 is a local privilege escalation vulnerability in the Zscaler Client Connector for macOS. The Zscaler Updater process fails to validate the digital signature of the installer before execution, allowing an attacker with local access to execute arbitrary code with the privileges of the updater process. This can lead to full system compromise. The vulnerability affects versions prior to 4.2. No public proof-of-concept or exploit code has been identified at this time.

CVSS Breakdown & Threat Level

• CVSS Score: 6.4 (Medium)
• Attack Vector (AV): Local (L) – The attacker must have local access to the system.
• Attack Complexity (AC): Low (L) – No special conditions are required.
• Privileges Required (PR): Low (L) – The attacker needs low-level privileges.
• User Interaction (UI): Required (R) – The user must perform some action (e.g., trigger the updater).
• Scope (S): Unchanged (U) – The vulnerability does not cross a trust boundary.
• Confidentiality (C): High (H) – Full data access possible.
• Integrity (I): High (H) – Full system modification possible.
• Availability (A): High (H) – Full system disruption possible.

Threat Level: Medium. While the CVSS score is moderate, the potential for full system compromise elevates the risk for enterprise environments.

Deep Dive & Mechanics

The vulnerability resides in the Zscaler Updater process on macOS. When the updater downloads and executes an installer package, it does not verify the digital signature of the installer. An attacker with local access can replace the legitimate installer with a malicious one. When the updater runs (either automatically or triggered by the user), it will execute the malicious code with the privileges of the updater process, which typically runs with elevated permissions.

Attack Flow:

1. Attacker gains local access to a macOS system running Zscaler Client Connector < 4.2.
2. Attacker identifies the location where the Zscaler Updater stores or downloads installer packages.
3. Attacker replaces the legitimate installer with a malicious payload.
4. The Zscaler Updater process executes the malicious installer, granting the attacker code execution with elevated privileges.

Vulnerable vs. Patched Code

Vulnerable Code (Conceptual): The updater process likely uses a function like NSTask or Process to execute the installer without verifying its code signature.

// Vulnerable: No signature check
- (void)runInstaller:(NSString *)installerPath {
    NSTask *task = [[NSTask alloc] init];
    [task setLaunchPath:@"/usr/sbin/installer"];
    [task setArguments:@[@"-pkg", installerPath, @"-target", @"/"]];
    [task launch];
    [task waitUntilExit];
}

Patched Code (Conceptual): The patched version adds a digital signature verification step before execution.

// Patched: Signature verification
- (void)runInstaller:(NSString *)installerPath {
    // Verify code signature
    NSTask *verifyTask = [[NSTask alloc] init];
    [verifyTask setLaunchPath:@"/usr/bin/codesign"];
    [verifyTask setArguments:@[@"-v", installerPath]];
    [verifyTask launch];
    [verifyTask waitUntilExit];
    if ([verifyTask terminationStatus] != 0) {
        // Signature invalid, abort
        return;
    }
    
    // Execute installer
    NSTask *task = [[NSTask alloc] init];
    [task setLaunchPath:@"/usr/sbin/installer"];
    [task setArguments:@[@"-pkg", installerPath, @"-target", @"/"]];
    [task launch];
    [task waitUntilExit];
}

Exploitation & Lab Setup

Red Team

Prerequisites:

• Local access to a macOS system with Zscaler Client Connector < 4.2.
• Ability to write to the directory where the updater stores installer packages.

Steps:

1. Identify the updater's working directory (e.g., /Library/Application Support/Zscaler/Updater/).
2. Create a malicious installer package (e.g., using pkgbuild or productbuild).
3. Replace the legitimate installer with the malicious one.
4. Trigger the updater (e.g., by restarting the Zscaler service or waiting for the scheduled update).

Example Malicious Package Creation:

# Create a postinstall script
cat > postinstall.sh << 'EOF'
#!/bin/bash
# Malicious payload
echo "pwned" > /tmp/pwned.txt
EOF
chmod +x postinstall.sh

# Build the package
pkgbuild --root /tmp/payload --scripts . --identifier com.zscaler.malicious --version 1.0 malicious.pkg

Blue Team

Detection:

• Monitor for unauthorized modifications to the Zscaler updater directory.
• Alert on execution of unsigned or untrusted installer packages.
• Use endpoint detection and response (EDR) to monitor for suspicious process execution chains.

Prevention:

• Ensure Zscaler Client Connector is updated to version 4.2 or later.
• Implement application whitelisting to prevent execution of unsigned code.
• Restrict write access to sensitive directories.

Indicators of Compromise (IOCs)

• File Hashes: (None publicly available)
• Process Names: Zscaler Updater, installer
• File Paths: /Library/Application Support/Zscaler/Updater/*.pkg
• Network Connections: Connections to Zscaler update servers (legitimate) or unknown IPs (malicious)
• Registry/Preferences: Modifications to Zscaler plist files

Detection Engineering

YARA Rule

rule CVE_2024_23460_Zscaler_Updater {
    meta:
        description = "Detects potential exploitation of CVE-2024-23460 via unsigned installer execution"
        author = "Valters IT"
        date = "2024-01-01"
        reference = "https://nvd.nist.gov/vuln/detail/CVE-2024-23460"
    strings:
        $s1 = "/usr/sbin/installer" ascii wide nocase
        $s2 = "-pkg" ascii wide nocase
        $s3 = "Zscaler" ascii wide nocase
    condition:
        all of them
}

Sigma Rule

title: CVE-2024-23460 - Zscaler Updater Unsigned Installer Execution
id: 12345678-1234-1234-1234-123456789012
status: experimental
description: Detects execution of installer without digital signature validation by Zscaler Updater
author: Valters IT
date: 2024-01-01
logsource:
    category: process_creation
    product: macos
detection:
    selection:
        Image|endswith: '/usr/sbin/installer'
        CommandLine|contains: '-pkg'
        ParentImage|endswith: '/Zscaler Updater'
    condition: selection
falsepositives:
    - Legitimate Zscaler updates
level: high

Suricata Rule

alert http $HOME_NET any -> $EXTERNAL_NET any (msg:"CVE-2024-23460 - Zscaler Updater Potential Malicious Download"; flow:to_server; content:"Zscaler"; http_client_body; content:".pkg"; http_client_body; classtype:attempted-user; sid:1000001; rev:1;)

Remediation & Mitigation

Immediate Actions:

1. Upgrade Zscaler Client Connector for macOS to version 4.2 or later.
2. Verify the digital signature of any installer packages before execution.
3. Restrict local user permissions to prevent unauthorized file modifications.

Long-term Measures:

• Implement code signing and verification for all software updates.
• Use endpoint detection and response (EDR) to monitor for suspicious behavior.
• Conduct regular security audits of third-party software.

Workarounds:

• If upgrade is not immediately possible, disable the Zscaler Updater service and manually apply updates after verifying their integrity.

Valters IT
DevSecOps & Cyber Threat Intelligence