CVE-2002-0714 in Squid
Summary
by MITRE
FTP proxy in Squid before 2.4.STABLE6 does not compare the IP addresses of control and data connections with the FTP server, which allows remote attackers to bypass firewall rules or spoof FTP server responses.
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Analysis
by VulDB Data Team • 11/23/2018
The vulnerability described in CVE-2002-0714 represents a critical security flaw in the Squid web proxy software that affects versions prior to 2.4.STABLE6. This issue specifically impacts the FTP proxy functionality within Squid, which serves as a gateway for FTP traffic between clients and FTP servers. The vulnerability stems from the proxy's failure to properly validate network connections, creating a pathway for malicious actors to exploit the system's trust model. The flaw exists in the manner in which Squid handles FTP control and data connections, particularly in how it manages IP address verification between these connection types. When an FTP proxy operates correctly, it should ensure that the data connection originates from the same IP address as the control connection to prevent unauthorized access or spoofing attempts. However, this validation mechanism was absent in affected versions, allowing attackers to manipulate the connection flow.
The technical implementation of this vulnerability lies in Squid's FTP proxy handling code where the software accepts FTP data connections without verifying that they originate from the same IP address as the corresponding control connection. This mismatch creates a scenario where an attacker can establish a control connection to a legitimate FTP server and then manipulate data connections to appear as if they originate from the target server. The flaw operates at the network protocol level, exploiting the trust relationship that exists between control and data connections in the FTP protocol. According to CWE-284, this vulnerability represents an improper access control issue where the system fails to properly authenticate the source of data connections. The weakness allows for a form of connection hijacking that bypasses the normal firewall protection mechanisms that administrators rely on to control access to FTP resources.
The operational impact of this vulnerability extends beyond simple bypassing of firewall rules, as it creates opportunities for various malicious activities including data interception, spoofing of FTP server responses, and potential access to restricted FTP resources. Attackers can exploit this flaw to gain unauthorized access to FTP servers that would normally be protected by firewall rules, effectively circumventing network security controls. The vulnerability can be particularly dangerous in environments where Squid is used as a gateway between internal networks and external FTP services, as it allows attackers to potentially access sensitive data or perform unauthorized operations on FTP servers. This issue can also enable man-in-the-middle attacks where attackers can intercept and modify FTP traffic between clients and servers, as the proxy no longer properly validates connection authenticity. The attack vector is particularly concerning because it requires minimal privileges and can be executed against any FTP proxy configuration that uses affected Squid versions.
Mitigation strategies for this vulnerability focus primarily on upgrading to Squid version 2.4.STABLE6 or later, where the proper IP address validation has been implemented. Organizations should also implement additional network security measures such as stricter firewall rules that limit access to FTP proxy services and monitor for unusual FTP connection patterns. Network administrators should consider implementing connection tracking mechanisms that can detect when control and data connections do not originate from the same source IP address. The solution aligns with ATT&CK technique T1071.004 which involves application layer protocol manipulation, and specifically addresses the lack of proper validation that allows attackers to manipulate connection flows. Security monitoring should include detection of anomalous FTP proxy behavior, particularly around connection establishment and data transfer phases where the IP address verification should occur. Regular security assessments and penetration testing should be conducted to ensure that proxy configurations properly enforce connection validation and that no other similar flaws exist in the network infrastructure.