CVE-2020-15152 in ftp-srv
Summary
by MITRE
ftp-srv versions 1.0.0 through 4.3.3 are vulnerable to Server-Side Request Forgery. The PORT command allows arbitrary IPs which can be used to cause the server to make a connection elsewhere. A possible workaround is blocking the PORT through the configuration. This issue is fixed in version 4.3.4. More information can be found on the linked advisory.
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Analysis
by VulDB Data Team • 11/10/2020
The vulnerability identified as CVE-2020-15152 affects ftp-srv versions 1.0.0 through 4.3.3 and represents a critical server-side request forgery vulnerability that exploits the FTP protocol's PORT command implementation. This flaw allows attackers to manipulate the FTP server's network behavior by specifying arbitrary IP addresses, potentially enabling unauthorized connections to external systems. The vulnerability stems from insufficient validation of IP addresses provided through the PORT command, which is a standard FTP command used to establish data connections between client and server. When an attacker sends a PORT command with a malicious IP address, the ftp-srv server processes this request without proper verification, creating an opportunity for malicious network activity.
The technical implementation of this vulnerability resides in the ftp-srv library's handling of the PORT command within its FTP server implementation. The PORT command in FTP protocol is designed to specify the IP address and port number where the server should connect to establish a data connection. However, in vulnerable versions, the server fails to validate the IP address provided in the PORT command against the originating client's IP address or other security constraints. This validation failure creates a pathway for attackers to redirect the server's outbound network connections to arbitrary destinations, potentially enabling access to internal systems, data exfiltration, or further network reconnaissance activities. The vulnerability directly maps to CWE-918, which describes server-side request forgery vulnerabilities where applications fail to validate or restrict the destinations of outbound requests.
The operational impact of this vulnerability extends beyond simple network connectivity issues, as it can enable attackers to bypass network segmentation and access systems that would normally be protected by firewalls or network access controls. An attacker could leverage this vulnerability to probe internal network services, attempt credential brute-forcing against internal systems, or establish connections to malicious servers controlled by the attacker. The potential for data exfiltration increases significantly when the FTP server has access to sensitive information or systems that are not properly isolated from external access. Organizations using ftp-srv in environments with restricted network access or those handling sensitive data face particularly high risk from this vulnerability. The issue creates a vector for lateral movement within networks and can potentially enable more sophisticated attack chains when combined with other vulnerabilities.
Mitigation strategies for CVE-2020-15152 should focus on immediate remediation through version updates to ftp-srv version 4.3.4 or later, which includes the necessary patches to address the PORT command validation issue. Organizations should also implement network-level controls to restrict FTP traffic and monitor for unusual PORT command usage patterns. The suggested workaround of blocking the PORT command through configuration settings provides a temporary solution while longer-term fixes are implemented. Security teams should also consider implementing network segmentation to limit the potential impact of successful exploitation attempts. Additionally, monitoring logs for suspicious PORT command usage and implementing intrusion detection systems can help identify exploitation attempts. The vulnerability demonstrates the importance of proper input validation and the potential security implications of protocol-level implementations that do not adequately consider the threat landscape. Organizations should also review their overall FTP server configurations and ensure that any services using ftp-srv are properly secured and monitored for similar vulnerabilities. The fix in version 4.3.4 addresses the core issue by implementing proper IP address validation for PORT command parameters, aligning with security best practices recommended by the ATT&CK framework for preventing command injection and server-side request forgery attacks.