CVE-2021-35245 in Serv-U Console
Summary
by MITRE • 12/06/2021
When a user has admin rights in Serv-U Console, the user can move, create and delete any files are able to be accessed on the Serv-U host machine.
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Analysis
by VulDB Data Team • 05/02/2025
The vulnerability identified as CVE-2021-35245 represents a critical privilege escalation and arbitrary file manipulation flaw within the Serv-U file transfer server software. This vulnerability specifically targets authenticated administrative users who possess elevated privileges within the Serv-U Console interface. The flaw allows these privileged users to execute unauthorized file operations including moving, creating, and deleting files on the underlying host system that would normally be restricted to authorized access only. The security implications extend beyond simple administrative functionality as this vulnerability essentially provides a path for privilege escalation and potential system compromise through unauthorized file system manipulation.
The technical nature of this vulnerability stems from inadequate access controls and authorization checks within the Serv-U Console administrative interface. When an administrator performs operations through the console, the system fails to properly validate or restrict file system operations against the underlying host machine. This creates a scenario where administrative privileges can be leveraged to perform file operations that exceed the intended scope of administrative duties. The vulnerability exists in the file system access layer of the Serv-U application where proper sandboxing or access boundary enforcement is missing. According to CWE classification, this vulnerability maps to CWE-284 Access Control Issues, specifically involving insufficient access control mechanisms that allow unauthorized file operations. The flaw demonstrates a lack of proper input validation and access control enforcement, which are fundamental security principles that should prevent administrative users from operating outside their designated boundaries.
The operational impact of CVE-2021-35245 is severe and multifaceted across enterprise environments that utilize Serv-U file transfer services. An attacker who gains administrative access to the Serv-U Console can leverage this vulnerability to establish persistent access points by creating malicious files, moving critical system files to evade detection, or deleting essential components to cause system disruption. The ability to delete files creates opportunities for data destruction attacks and can be combined with file creation capabilities to establish backdoors or malware persistence mechanisms. Additionally, the privilege escalation potential means that even users with limited initial access could potentially exploit this vulnerability to gain broader system control. Organizations using Serv-U in production environments face significant risk of data compromise, system availability issues, and potential lateral movement within their network infrastructure. The vulnerability can be exploited to target sensitive data repositories, system configuration files, or even critical infrastructure components that are accessible through the Serv-U host system.
Mitigation strategies for CVE-2021-35245 should prioritize immediate patching of affected Serv-U installations to address the underlying access control implementation flaws. Organizations must implement strict administrative access controls and monitoring of Serv-U console activities to detect unauthorized file operations. Network segmentation and principle of least privilege should be enforced to limit the scope of potential exploitation. The implementation of file integrity monitoring solutions can help detect unauthorized file changes that may result from exploitation of this vulnerability. Security teams should also conduct comprehensive audits of Serv-U configurations and administrative user permissions to ensure that only necessary users have administrative access. According to ATT&CK framework, this vulnerability maps to T1078 Valid Accounts and T1486 Data Encrypted for Impact, as it enables unauthorized access to system resources and potential data destruction. Regular security assessments and penetration testing should be conducted to identify similar access control weaknesses in other enterprise applications and file transfer systems. Additionally, implementing multi-factor authentication for administrative access and maintaining detailed logging of all file system operations within Serv-U environments will provide crucial forensic capabilities for detecting and responding to exploitation attempts.