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The vulnerability identified as CVE-2015-3306 exists within the mod_copy module of ProFTPD version 1.3.5.
This specific module implements the SITE CPFR and SITE CPTO FTP commands on the server.
These commands are designed to allow copying files or directories from one location to another directly.
However, the module fails to properly validate or restrict user permissions and input paths.
As a result, unauthenticated remote attackers can leverage these site commands to interact with the file system.
An attacker can specify an arbitrary source path using the SITE CPFR command without any authentication.
Following that, they can specify an arbitrary destination path using the SITE CPTO command.
This flawed implementation permits reading arbitrary files from the underlying server filesystem.
It also enables writing arbitrary content or files to sensitive locations on the server.
By combining file write capabilities with web root access, attackers can upload malicious scripts.
For instance, an attacker can copy a payload or read sensitive system configuration files.
Once a malicious script is written to the web root, it can be executed remotely via HTTP.
This leads directly to remote code execution and full system compromise by external actors.
The lack of authentication requirements makes this vulnerability exceptionally dangerous in practice.
Any external user with network access to the FTP service can exploit it instantly.
No prior credentials or valid user accounts are required to initiate the attack sequence.
The flaw bypasses standard file access controls implemented by the operating system.
It misuses the privileges under which the ProFTPD daemon process runs on the host.
Typically, if ProFTPD runs with elevated privileges, the overall impact is severe.
Vendor advisories and exploit frameworks quickly integrated proof-of-concepts after public discovery.
Security researchers demonstrated multiple attack vectors utilizing these site commands.
Remediation requires upgrading the software to patched versions or disabling the mod_copy module.
System administrators must audit their FTP server configurations to prevent unauthorized access.
Failing to address this flaw leaves infrastructure completely exposed to malicious takeover.
The simplicity of the command sequence makes automated exploitation trivial for threat actors.
Network intrusion detection systems often look for suspicious SITE CPFR and SITE CPTO strings.
Understanding this mechanism highlights the importance of strict input validation in FTP extensions.
DailyCVE Form:
Platform: ProFTPD
Version: 1.3.5
Vulnerability: Arbitrary file access
Severity: Critical
date: May 18 2015
Prediction: May 2015 patched
What Undercode Say:
Connecting to the vulnerable FTP service nc target_ip 21 Exploiting mod_copy to read arbitrary files SITE CPFR /etc/passwd SITE CPTO /tmp/passwd.txt Writing a malicious PHP backdoor into the web root SITE CPFR /proc/self/cmdline SITE CPTO /var/www/html/backdoor.php
Exploit: (Educational Purposes!)
The exploit leverages the unauthenticated mod_copy module commands SITE CPFR (Copy From) and SITE CPTO (Copy To). Attackers connect to the target FTP server and issue a SITE CPFR command pointing to any readable file on the filesystem (such as system logs, configuration files, or proc entries). Immediately following, they issue a SITE CPTO command specifying a destination path they control, such as a web-accessible directory. This allows the attacker to clone files, exfiltrate sensitive data, or drop executable web shells to achieve remote code execution without providing any valid user credentials.
Protection: from this CVE
Upgrade the ProFTPD server software to version 1.3.5a, 1.3.6rc1, or any later secured release where the mod_copy vulnerability is resolved. If upgrading is not immediately feasible, disable the mod_copy module entirely within the ProFTPD configuration file by removing or commenting out the module loading directive for mod_copy.c, and restart the FTP service. Additionally, implement strict firewall rules and network segmentation to restrict unauthorized access to FTP ports.
Impact:
Remote unauthenticated attackers can fully compromise the affected server, read sensitive system files containing credentials or configuration data, write arbitrary malicious payloads to web root directories, execute arbitrary system commands, and pivot further into internal corporate or cloud networks.
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Sources:
Reported By: www.cve.org
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