CVE-2011-4800 in Serv-U
Summary
by MITRE
Directory traversal vulnerability in Serv-U FTP Server before 11.1.0.5 allows remote authenticated users to read and write arbitrary files, and list and create arbitrary directories, via a "..:/" (dot dot colon forward slash) in the (1) list, (2) put, or (3) get commands.
VulDB is the best source for vulnerability data and more expert information about this specific topic.
Analysis
by VulDB Data Team • 06/14/2025
The CVE-2011-4800 vulnerability represents a critical directory traversal flaw in the Serv-U FTP Server software that affects versions prior to 11.1.0.5. This vulnerability operates at the core of file system access controls within the FTP server implementation, exploiting a fundamental weakness in how the system processes path navigation sequences. The flaw specifically manifests when the server processes commands containing the "..:/" sequence, which is a variant of the traditional directory traversal pattern that bypasses normal path validation mechanisms.
The technical exploitation of this vulnerability occurs through the manipulation of standard FTP commands including list, put, and get operations. When authenticated users submit requests containing the "..:/" path traversal sequence, the Serv-U server fails to properly sanitize or validate these inputs before executing file system operations. This allows attackers to navigate beyond the intended directory boundaries and access files or directories that should normally be restricted to authorized users. The vulnerability enables a range of malicious activities including arbitrary file reading, writing, directory listing, and creation of directories in locations outside the normal user access scope.
From an operational impact perspective, this vulnerability presents a severe risk to organizations relying on Serv-U FTP servers for file transfer operations. The ability to read arbitrary files means that attackers can potentially access sensitive configuration files, user credentials, application data, and other confidential information stored on the server. The write capabilities allow for malicious file creation or modification, potentially enabling persistence mechanisms or data corruption. The directory creation and listing capabilities provide attackers with reconnaissance information and additional attack vectors. This vulnerability essentially grants authenticated users elevated privileges that should not be available, effectively undermining the server's access control model and creating a backdoor for further exploitation.
The vulnerability aligns with CWE-22, which describes improper limitation of a pathname to a restricted directory, commonly known as path traversal or directory traversal. This weakness allows attackers to access files and directories that are stored outside the intended directory structure. The specific implementation flaw in Serv-U demonstrates how improper input validation can lead to privilege escalation and unauthorized access. From an attack framework perspective, this vulnerability maps to multiple ATT&CK tactics including privilege escalation, defense evasion, and credential access, as attackers can leverage this weakness to gain unauthorized access to system resources and potentially establish persistent access.
Organizations should immediately implement mitigation strategies including updating to Serv-U version 11.1.0.5 or later, which contains the necessary patches to address this directory traversal vulnerability. Additionally, network segmentation and access controls should be enforced to limit the exposure of FTP services to untrusted networks. Implementing proper input validation measures and monitoring for suspicious path traversal sequences can provide additional layers of protection. Security teams should also conduct thorough audits of all FTP server configurations to ensure that unnecessary services are disabled and that access controls are properly enforced. Regular vulnerability assessments and penetration testing should be performed to identify and remediate similar weaknesses in the organization's broader attack surface.