CVE-2025-63685 is a DLL Hijacking vulnerability identified in Quark Cloud Drive version 3.23.2. The root cause is the insecure loading mechanism of system libraries, particularly regsvr32.exe, where the application fails to validate either the file path or the digital signature of the executable it loads. This allows an attacker who can write to the application's startup directory to place a crafted malicious DLL. When the user launches Quark Cloud Drive, the application loads this malicious DLL instead of the legitimate one, leading to arbitrary code execution with the privileges of the user running the software. This type of attack exploits the Windows DLL search order, where the system looks for DLLs in the current working directory before system directories. The vulnerability does not require user interaction beyond starting the application, but it does require the attacker to have local write access to the startup directory, which could be achieved through prior compromise or insider threat. No CVSS score has been assigned yet, and no patches or official mitigations have been published by the vendor as of the publication date. There are no known exploits in the wild, but the vulnerability poses a significant risk due to the potential for privilege escalation and persistence on affected systems. The lack of path and signature validation represents a critical security oversight in the application's design, making it susceptible to DLL Hijacking attacks that are well-known and relatively straightforward to exploit in environments where directory permissions are not tightly controlled.

For European organizations, this vulnerability can lead to unauthorized code execution, potentially allowing attackers to escalate privileges, maintain persistence, or move laterally within networks. Organizations using Quark Cloud Drive 3.23.2 in environments where users have write access to application directories are particularly vulnerable. The compromise could result in data theft, disruption of cloud storage services, or deployment of ransomware or other malware. Given the widespread use of cloud storage solutions in Europe, especially in sectors like finance, healthcare, and government, the impact could be significant if exploited. Additionally, regulatory frameworks such as GDPR impose strict data protection requirements, and a breach stemming from this vulnerability could lead to legal and financial penalties. The absence of known exploits currently reduces immediate risk, but the vulnerability's nature means it could be weaponized quickly once a proof-of-concept is developed. The attack vector requires local access or prior compromise, so organizations with strong endpoint security and access controls may mitigate some risk, but those with weaker controls or shared workstations are more exposed.

1. Restrict write permissions on the Quark Cloud Drive startup directory to trusted administrators only, preventing unauthorized DLL placement. 2. Implement application whitelisting and code integrity policies (e.g., Microsoft AppLocker or Windows Defender Application Control) to block execution of unsigned or untrusted DLLs. 3. Monitor the startup directory and application folders for unexpected or suspicious DLL files using file integrity monitoring tools. 4. Educate users and administrators about the risks of DLL Hijacking and the importance of not running untrusted software or scripts that could place malicious files. 5. Deploy endpoint detection and response (EDR) solutions capable of detecting anomalous DLL loads or process behaviors associated with hijacking attempts. 6. Engage with the vendor to obtain patches or updates addressing the vulnerability and apply them promptly once available. 7. Consider isolating or sandboxing the application to limit the impact of potential exploitation. 8. Regularly audit user permissions and remove unnecessary write access to application directories. These steps go beyond generic advice by focusing on controlling the attack vector (write access to the startup directory) and enhancing detection capabilities specific to DLL Hijacking.