CVE-2025-63685: Quark Cloud Drive RCE Vulnerability

CVE-2025-63685 Overview

CVE-2025-63685 is a DLL Hijacking vulnerability affecting Quark Cloud Drive v3.23.2. This vulnerability stems from the insecure loading of system libraries, where the application does not validate the path or signature of regsvr32.exe it loads. An attacker can place a crafted malicious DLL in the application's startup directory, which will be loaded and executed when the user launches the program.

Critical Impact

This DLL Hijacking vulnerability enables attackers to achieve arbitrary code execution with the privileges of the user running Quark Cloud Drive by placing a malicious DLL in the application's startup directory.

Affected Products

• Quark Cloud Drive version 3.23.2
• quark:quark_cloud_drive (CPE: cpe:2.3:a:quark:quark_cloud_drive:3.23.2:*:*:*:*:*:*:*)

Discovery Timeline

• 2025-11-20 - CVE-2025-63685 published to NVD
• 2025-12-16 - Last updated in NVD database

Technical Details for CVE-2025-63685

Vulnerability Analysis

This vulnerability is classified under CWE-491 (Public cloneable() Method Without Final), though the core issue relates to insecure DLL loading practices. The application fails to properly validate the integrity and origin of dynamically loaded libraries during startup. When Quark Cloud Drive launches, it attempts to load regsvr32.exe without verifying the file path or digital signature, creating an opportunity for attackers to inject malicious code.

The network-based attack vector combined with no required privileges or user interaction makes this vulnerability particularly dangerous. An attacker with the ability to write files to the application's startup directory can achieve complete system compromise through arbitrary code execution.

Root Cause

The root cause of this vulnerability lies in the application's failure to implement secure library loading practices. Specifically, Quark Cloud Drive does not:

1. Validate the full path of loaded executables and DLLs
2. Verify digital signatures before loading system components
3. Implement proper search order hardening for dynamic library resolution

This allows the Windows DLL search order to be exploited, where a malicious DLL placed in the application directory takes precedence over legitimate system libraries.

Attack Vector

The attack requires placing a malicious DLL file in Quark Cloud Drive's startup directory. When a user launches the application, the malicious DLL is loaded before the legitimate system library, allowing the attacker's code to execute with the same privileges as the application.

The exploitation mechanism follows these steps:

1. Attacker gains write access to the Quark Cloud Drive installation or startup directory
2. Attacker places a crafted malicious DLL designed to mimic a legitimate system library
3. When the victim launches Quark Cloud Drive, the application loads the malicious DLL
4. The malicious code executes with the user's privileges, potentially leading to full system compromise

Additional technical details regarding this vulnerability can be found in the GitHub CVE Issue Discussion.

Detection Methods for CVE-2025-63685

Indicators of Compromise

• Unexpected DLL files present in the Quark Cloud Drive installation directory or startup folders
• DLL files without valid digital signatures in application directories
• Unusual process execution spawned from QuarkCloudDrive.exe or related processes
• Network connections originating from Quark Cloud Drive processes to unexpected destinations

Detection Strategies

• Monitor file system activity for new DLL files being written to Quark Cloud Drive installation directories
• Implement application whitelisting to detect and block unauthorized DLL loading
• Use endpoint detection tools to identify DLL side-loading or hijacking attempts
• Enable Windows Sysmon logging to capture DLL load events (Event ID 7) from Quark Cloud Drive processes

Monitoring Recommendations

• Configure SentinelOne to monitor for suspicious DLL loading behavior from cloud storage applications
• Set up alerts for modifications to the Quark Cloud Drive installation directory
• Implement file integrity monitoring for application directories to detect unauthorized changes
• Monitor for execution of regsvr32.exe from unexpected locations or with unusual parameters

How to Mitigate CVE-2025-63685

Immediate Actions Required

• Restrict write permissions to the Quark Cloud Drive installation and startup directories
• Implement application whitelisting to prevent unauthorized DLL execution
• Monitor for and remove any suspicious DLL files in application directories
• Consider temporarily disabling Quark Cloud Drive until a vendor patch is available

Patch Information

As of the last update on 2025-12-16, no official patch information has been published by Quark. Organizations should monitor vendor communications and the GitHub CVE Issue Discussion for updates regarding security fixes.

Workarounds

• Apply the principle of least privilege to user accounts running Quark Cloud Drive
• Use Group Policy to enforce DLL search order hardening
• Implement application control solutions to block unsigned DLLs from loading
• Run Quark Cloud Drive in a sandboxed environment to limit potential impact

# Windows Group Policy configuration for DLL search order hardening
# Enable SafeDllSearchMode via Registry
reg add "HKEY_LOCAL_MACHINE\System\CurrentControlSet\Control\Session Manager" /v SafeDllSearchMode /t REG_DWORD /d 1 /f

# Restrict write access to Quark Cloud Drive installation directory
icacls "C:\Program Files\Quark Cloud Drive" /inheritance:r /grant:r "SYSTEM:(OI)(CI)F" /grant:r "Administrators:(OI)(CI)F" /grant:r "Users:(OI)(CI)RX"