CVE-2025-63685 is a critical DLL hijacking vulnerability affecting Quark Cloud Drive version 3.23.2. The root cause is the application's failure to securely load the system utility regsvr32.exe. Specifically, the application does not validate the file path or verify the digital signature of regsvr32.exe before loading it. This insecure loading mechanism allows an attacker to place a crafted malicious DLL in the same directory from which the application starts. When the user launches Quark Cloud Drive, the application inadvertently loads and executes the malicious DLL, resulting in arbitrary code execution under the context of the logged-in user. The vulnerability is classified under CWE-491 (Insecure Loading of DLL). The CVSS v3.1 base score is 9.8, reflecting that the attack vector is network-based (AV:N), requires no privileges (PR:N), no user interaction (UI:N), and impacts confidentiality, integrity, and availability at a high level (C:H/I:H/A:H). Although no exploits have been reported in the wild yet, the ease of exploitation and critical impact make this a severe threat. The lack of patch information suggests that a fix is not yet publicly available, increasing urgency for defensive measures. This vulnerability is particularly dangerous in environments where Quark Cloud Drive is used to manage or synchronize sensitive cloud data, as attackers could gain persistent access or disrupt operations.

For European organizations, the impact of CVE-2025-63685 can be severe. Successful exploitation allows attackers to execute arbitrary code with user-level privileges, potentially leading to full system compromise if the user has elevated rights. This can result in data theft, unauthorized access to cloud storage, ransomware deployment, or disruption of cloud synchronization services. Organizations relying on Quark Cloud Drive for critical business operations or handling sensitive personal data (e.g., GDPR-regulated information) face risks of data breaches and compliance violations. The vulnerability's network attack vector means remote exploitation is possible, increasing the threat surface. Additionally, the lack of user interaction or authentication requirements facilitates automated or mass exploitation attempts. The potential for lateral movement within corporate networks and persistence through cloud synchronization mechanisms further exacerbates the threat. European sectors such as finance, healthcare, and government, which often use cloud storage solutions, are particularly vulnerable to operational disruption and reputational damage.

To mitigate CVE-2025-63685, organizations should implement the following specific measures: 1) Restrict write permissions on the Quark Cloud Drive startup directory to prevent unauthorized DLL placement. 2) Employ application whitelisting or allowlisting to ensure only trusted executables and DLLs are loaded. 3) Monitor the startup directory and related paths for unexpected or suspicious DLL files using file integrity monitoring tools. 4) Use endpoint detection and response (EDR) solutions to detect anomalous process creation involving regsvr32.exe or unexpected DLL loads. 5) If possible, configure the application or system to load system libraries only from trusted system directories, avoiding relative or current directory loading. 6) Engage with the vendor to obtain patches or updates addressing the vulnerability and apply them promptly once available. 7) Educate users about the risks of running untrusted software and maintain least privilege principles to limit the impact of code execution. 8) Network segmentation can limit the spread of an attacker who gains initial access via this vulnerability. These targeted actions go beyond generic advice by focusing on controlling DLL loading behavior and monitoring for exploitation indicators specific to this vulnerability.