CVE-2000-1027 in PIX
Summary
by MITRE
Cisco Secure PIX Firewall 5.2(2) allows remote attackers to determine the real IP address of a target FTP server by flooding the server with PASV requests, which includes the real IP address in the response when passive mode is established.
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Analysis
by VulDB Data Team • 09/23/2024
This vulnerability resides in the Cisco Secure PIX Firewall version 5.2(2) and represents a significant information disclosure flaw that undermines network security through improper handling of FTP passive mode connections. The vulnerability specifically affects the firewall's processing of PASV (Passive) FTP commands where the firewall fails to properly sanitize or mask the real IP address of backend servers. When an attacker sends multiple PASV requests to an FTP server protected by this vulnerable firewall, the firewall includes the actual server IP address in its response, effectively leaking internal network topology information. This behavior violates fundamental security principles of network segmentation and server concealment that are essential for maintaining operational security and preventing reconnaissance activities.
The technical implementation of this vulnerability stems from the firewall's inadequate handling of FTP protocol interactions during passive mode establishment. In standard FTP operations, when a client connects to an FTP server in passive mode, the server responds with a PASV command that includes an IP address and port number for data connection establishment. The vulnerability occurs because the Cisco PIX firewall in version 5.2(2) does not properly filter or replace the real IP address in these responses, instead forwarding the original server IP address directly to the attacker. This flaw operates at the application layer protocol handling level and represents a classic case of insufficient input validation and output sanitization, which aligns with CWE-20 - Improper Input Validation and CWE-200 - Information Exposure. The vulnerability is particularly concerning as it operates at the network perimeter where the firewall acts as a gateway between internal and external networks, making it a prime target for reconnaissance activities.
The operational impact of this vulnerability extends beyond simple information disclosure, creating potential pathways for more sophisticated attacks within the network infrastructure. An attacker who successfully exploits this vulnerability gains knowledge of internal server IP addresses, which can be used to construct more targeted attacks against specific systems or to map internal network structures. This information can facilitate subsequent exploitation attempts such as port scanning, service enumeration, or even direct attacks against the identified servers. The vulnerability also impacts the firewall's ability to provide effective network isolation, as it fails to properly obscure the internal network topology from external observers. According to ATT&CK framework, this vulnerability relates to T1046 - Network Service Scanning and T1083 - File and Directory Discovery, as it enables attackers to gather network mapping information and potentially identify target systems for further exploitation.
Mitigation strategies for this vulnerability should focus on immediate firewall configuration updates and network architecture improvements. The primary solution involves upgrading to a patched version of the Cisco PIX Firewall software where the vulnerability has been addressed through proper IP address sanitization in FTP response handling. Organizations should also implement network segmentation strategies that limit direct exposure of internal FTP servers to external networks and consider deploying additional layers of security controls such as deep packet inspection or application layer filtering. Network administrators should also monitor FTP traffic patterns for unusual PASV request sequences that might indicate exploitation attempts. The vulnerability highlights the importance of proper protocol handling in security devices and demonstrates how seemingly minor implementation flaws can have significant security implications. Regular security assessments and vulnerability scanning should be conducted to identify similar issues in other network security appliances and ensure that all components maintain proper information hiding mechanisms to prevent unauthorized disclosure of internal network information.