CVE-2025-66449 is a path traversal vulnerability classified under CWE-22, CWE-73, and CWE-434 affecting C4illin's ConvertX, a self-hosted online file converter. The vulnerability exists in versions prior to 0.16.0 within the /upload endpoint, which accepts a file upload request from authenticated users. The core issue is that the application directly uses the user-supplied file.name parameter without any sanitization or validation, allowing attackers to craft file paths that traverse directories and write files outside the intended upload directory. This arbitrary file write capability can be exploited to overwrite critical system binaries or application files, effectively enabling remote code execution with the privileges of the ConvertX service. The vulnerability does not require user interaction beyond authentication, and the attack surface is network-exposed since the service is self-hosted and accessible over HTTP/S. The CVSS v3.1 score of 8.8 reflects the high impact on confidentiality, integrity, and availability, combined with low attack complexity and no user interaction. The vendor has addressed the issue in version 0.16.0 by implementing proper input validation and sanitization of file paths to restrict file writes to authorized directories. No public exploits have been observed yet, but the vulnerability poses a significant risk if left unpatched, especially in environments where ConvertX is deployed with elevated privileges or on critical infrastructure.

For European organizations, exploitation of this vulnerability could lead to full system compromise of servers running vulnerable ConvertX versions. This could result in unauthorized access to sensitive data, disruption of file conversion services, and potential lateral movement within internal networks. Critical sectors such as finance, healthcare, and government agencies that rely on file conversion workflows may face operational downtime and data breaches. The ability to overwrite system binaries elevates the risk to complete system takeover, which could be leveraged for espionage, ransomware deployment, or sabotage. Given the self-hosted nature of ConvertX, organizations with less mature patch management or weaker authentication controls are particularly vulnerable. The lack of known exploits in the wild currently reduces immediate risk but does not diminish the urgency for remediation. Attackers targeting European entities could exploit this vulnerability to gain footholds in networks, especially where ConvertX is integrated into automated document processing pipelines.

European organizations should immediately upgrade ConvertX installations to version 0.16.0 or later to apply the official patch. Until upgrades are completed, restrict access to the /upload endpoint using network segmentation and firewall rules to limit exposure to trusted users only. Implement strong authentication mechanisms, such as multi-factor authentication, to reduce the risk of credential compromise. Conduct thorough audits of file upload logs to detect suspicious file names or unauthorized file writes. Employ host-based intrusion detection systems (HIDS) to monitor critical system binaries for unauthorized changes. Additionally, apply application-layer input validation and sanitization as an extra defense layer if upgrading is delayed. Regularly back up critical data and system configurations to enable recovery in case of compromise. Finally, educate administrators and users about the risks of uploading files with malicious names and enforce the principle of least privilege for the ConvertX service account to limit potential damage.