1. Introduction
The ArGoSoft FTP Server RNTO Command Remote Buffer Overflow vulnerability affects FTP servers running the ArGoSoft software. This flaw allows an attacker to crash the server, potentially leading to a denial of service, or even execute arbitrary code on the system. Systems commonly affected are those hosting publicly accessible FTP services or internal file shares using this software. A successful exploit could compromise confidentiality, integrity and availability of data.
2. Technical Explanation
The vulnerability is caused by a buffer overflow in how ArGoSoft FTP Server handles the RNTO (Rename) command. An authenticated user can send a specially crafted RNTO command that exceeds the allocated buffer size, overwriting adjacent memory and potentially gaining control of the application or system. The CVE associated with this issue is CVE-2006-2170.
- Root cause: Insufficient input validation when processing the RNTO command allows for a buffer overflow.
- Exploit mechanism: An attacker sends an RNTO command containing a string longer than the expected buffer size, overwriting memory and potentially executing arbitrary code. For example, sending “RNTO verylongfilename” could trigger the overflow.
- Scope: ArGoSoft FTP Server for Windows is affected. Specific versions are not explicitly stated in available documentation but the bug report dates back to 2006.
3. Detection and Assessment
To confirm whether a system is vulnerable, first check the installed version of ArGoSoft FTP Server. A thorough assessment involves monitoring network traffic for suspicious RNTO commands.
- Quick checks: Check the application’s “About” box or use the command line to display the version information.
- Scanning: Nessus plugin ID 17789 can detect this vulnerability, but results should be verified manually.
- Logs and evidence: Examine FTP server logs for unusual RNTO commands or errors related to buffer overflows. Look for entries containing “RNTO” with excessively long filenames.
4. Solution / Remediation Steps
Due to the age of this vulnerability, a patch may not be readily available. Mitigation focuses on minimizing exposure and monitoring for attacks.
4.1 Preparation
- Stop the ArGoSoft FTP Server service to prevent new connections during remediation. A roll back plan involves restoring the backup or reverting the system snapshot.
- Changes should be performed during a scheduled maintenance window with appropriate approval from IT management.
4.2 Implementation
- Step 1: Disable anonymous access to the FTP server if it is not required. This limits potential attackers.
- Step 2: Implement strong password policies for all authenticated users.
- Step 3: Monitor FTP server logs closely for suspicious activity, especially RNTO commands.
4.3 Config or Code Example
Before
Allow anonymous access = Yes
After
Allow anonymous access = No
4.4 Security Practices Relevant to This Vulnerability
Several security practices can help mitigate this vulnerability type.
- Practice 1: Least privilege – restrict user accounts to only the necessary permissions, reducing the impact of a successful exploit.
- Practice 2: Input validation – implement strict input validation on all data received by the FTP server to prevent buffer overflows and other injection attacks.
4.5 Automation (Optional)
No specific automation script is available for this vulnerability due to its age.
5. Verification / Validation
Confirm the fix by verifying that anonymous access is disabled and monitoring logs for suspicious activity.
- Post-fix check: Check the FTP server configuration file to confirm that anonymous access is set to “No”.
- Re-test: Attempt an anonymous connection to the FTP server. It should be rejected.
- Smoke test: Verify that authenticated users can still connect and transfer files as expected.
- Monitoring: Monitor FTP server logs for failed login attempts or suspicious RNTO commands.
Configuration file shows "Allow anonymous access = No"
6. Preventive Measures and Monitoring
Regular security assessments and patch management are crucial for preventing similar vulnerabilities.
- Baselines: Update a security baseline or policy to include disabling anonymous FTP access and enforcing strong password policies.
- Pipelines: Implement static analysis tools in the CI/CD pipeline to identify potential buffer overflows during development.
- Asset and patch process: Establish a regular patch review cycle for all software, including FTP servers.
7. Risks, Side Effects, and Roll Back
Disabling anonymous access may disrupt legitimate users if it was previously allowed. Rolling back involves re-enabling anonymous access in the configuration file.
- Risk or side effect 1: Disabling anonymous access could break existing workflows that rely on it.
- Risk or side effect 2: Incorrectly configured firewall rules may prevent legitimate users from accessing the FTP server.
- Roll back: Step 1: Re-enable anonymous access in the FTP server configuration file. Step 2: Restart the ArGoSoft FTP Server service.
8. References and Resources
Links to resources related to this specific vulnerability.
- Vendor advisory or bulletin: No official vendor advisory available.
- NVD or CVE entry: https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2006-2170
- Product or platform documentation relevant to the fix: https://seclists.org/bugtraq/2006/May/22