CVE-2025-3928 is a high-severity vulnerability affecting the Commvault Web Server, a component used in Commvault's data management and backup solutions. The vulnerability allows a remote attacker with authenticated access to compromise the web server by creating and executing webshells. Webshells are malicious scripts that provide attackers with a backdoor into the server, enabling them to execute arbitrary commands, escalate privileges, and potentially move laterally within the network. The vulnerability affects multiple versions of the Commvault Web Server, specifically versions 11.36.0, 11.32.0, 11.28.0, and 11.20.0 on both Windows and Linux platforms. The issue was addressed in patched versions 11.36.46, 11.32.89, 11.28.141, and 11.20.217. The CVSS v3.1 score of 8.8 reflects the high impact on confidentiality, integrity, and availability, with an attack vector over the network, low attack complexity, and requiring privileges but no user interaction. The vulnerability was added to the CISA Known Exploited Vulnerabilities Catalog on April 28, 2025, indicating recognition of its criticality and potential for exploitation, although no active exploits have been reported in the wild yet. The lack of detailed technical information limits precise understanding of the exploitation mechanism, but the advisory clearly states the risk of webshell deployment, which is a common and dangerous attack vector in web server compromises.

For European organizations, the impact of this vulnerability is significant due to Commvault's widespread use in enterprise backup and data management environments. Successful exploitation could lead to unauthorized access to sensitive backup data, manipulation or deletion of backups, and disruption of data recovery processes, severely affecting business continuity and data integrity. Confidentiality breaches could expose personal data protected under GDPR, leading to regulatory penalties and reputational damage. Integrity and availability impacts could result in operational downtime and loss of trust in data protection mechanisms. The requirement for authenticated access means attackers may need to compromise credentials first, but once inside, the ability to deploy webshells can facilitate persistent and stealthy control over critical infrastructure. This is particularly concerning for sectors with stringent data protection needs such as finance, healthcare, and government agencies across Europe.

European organizations should immediately verify their Commvault Web Server versions and apply the vendor-provided patches (versions 11.36.46, 11.32.89, 11.28.141, or 11.20.217) without delay. Beyond patching, organizations should enforce strict access controls and multi-factor authentication (MFA) for all users with access to the Commvault web interface to reduce the risk of credential compromise. Regularly audit and monitor web server logs for unusual activity indicative of webshell deployment or command execution. Implement network segmentation to isolate backup infrastructure from general user networks and limit exposure. Employ application whitelisting and endpoint detection and response (EDR) tools to detect and block unauthorized script execution. Conduct periodic security assessments and penetration tests focusing on backup infrastructure to identify potential weaknesses. Finally, maintain robust incident response plans tailored to backup system compromises to ensure rapid containment and recovery.