CVE-2004-2111 in Serv-U
Summary
by MITRE
Stack-based buffer overflow in the site chmod command in Serv-U FTP Server before 4.2 allows remote attackers to execute arbitrary code via a long filename.
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Analysis
by VulDB Data Team • 10/05/2025
The vulnerability described in CVE-2004-2111 represents a critical stack-based buffer overflow flaw within the Serv-U FTP Server software version 4.2 and earlier. This issue specifically affects the site chmod command implementation, which is responsible for changing file permissions within the FTP server environment. The vulnerability arises from insufficient input validation when processing filenames provided by remote clients, creating an exploitable condition that can be leveraged by malicious actors to gain unauthorized system access.
The technical nature of this flaw stems from improper bounds checking within the command processing routine that handles file permission changes. When a remote attacker submits a specially crafted filename exceeding the allocated buffer space, the excessive data overflows into adjacent memory locations, potentially corrupting critical program state information. This type of vulnerability falls under CWE-121, which specifically addresses stack-based buffer overflow conditions where insufficient boundary checks allow attackers to overwrite stack data. The overflow can overwrite return addresses, function pointers, or other critical control data, enabling arbitrary code execution.
The operational impact of this vulnerability is severe and far-reaching for organizations utilizing affected Serv-U FTP Server versions. Remote attackers can exploit this weakness without requiring authentication, making it particularly dangerous in environments where FTP services are exposed to the internet. Successful exploitation allows attackers to execute malicious code with the privileges of the FTP server process, potentially leading to complete system compromise, data theft, or establishment of persistent backdoors. The vulnerability affects the core functionality of the file transfer service, making it a prime target for attackers seeking to gain unauthorized access to network resources.
Organizations should implement immediate mitigations including upgrading to Serv-U FTP Server version 4.2 or later, which contains the necessary patches to address this buffer overflow condition. Network segmentation and firewall rules should be implemented to restrict access to FTP services, particularly when they are exposed to untrusted networks. Additionally, monitoring for suspicious filename patterns and implementing intrusion detection systems can help identify exploitation attempts. From an ATT&CK framework perspective, this vulnerability maps to T1078 for valid accounts and T1059 for command and scripting interpreter, as attackers can leverage the compromised service to execute commands and maintain persistence within the target environment. Regular security assessments and vulnerability scanning should be conducted to identify similar issues in legacy systems and ensure comprehensive protection against similar exploitation techniques.