CVE-2018-0087 in Web Security Appliance
Summary
by MITRE
A vulnerability in the FTP server of the Cisco Web Security Appliance (WSA) could allow an unauthenticated, remote attacker to log in to the FTP server of the device without a valid password. The attacker does need to have a valid username. The vulnerability is due to incorrect FTP user credential validation. An attacker could exploit this vulnerability by using FTP to connect to the management IP address of the targeted device. A successful exploit could allow the attacker to log in to the FTP server of the Cisco WSA without having a valid password. This vulnerability affects Cisco AsyncOS for WSA Software on both virtual and hardware appliances that are running any release of Cisco AsyncOS 10.5.1 for WSA Software. The device is vulnerable only if FTP is enabled on the management interface. FTP is disabled by default. Cisco Bug IDs: CSCvf74281.
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Analysis
by VulDB Data Team • 02/17/2023
The vulnerability described in CVE-2018-0087 represents a critical authentication bypass flaw within the FTP server implementation of Cisco Web Security Appliance (WSA) devices. This weakness stems from improper validation of user credentials during the FTP authentication process, creating a significant security risk for organizations relying on these appliances for network security. The vulnerability specifically affects Cisco AsyncOS for WSA Software versions running on both virtual and physical hardware deployments, making it particularly concerning given the widespread adoption of WSA appliances in enterprise environments. The flaw manifests when the FTP service is enabled on the management interface, which remains disabled by default, indicating that the vulnerability requires a specific configuration state to be exploitable.
The technical nature of this vulnerability falls under CWE-287, which addresses improper handling of authentication credentials, and more specifically aligns with improper authentication mechanisms that allow attackers to bypass standard authentication procedures. Attackers can exploit this weakness by establishing an FTP connection to the management IP address of the targeted WSA device, utilizing a valid username to attempt authentication without providing a legitimate password. This type of attack directly violates the fundamental principles of authentication security where both username and password should be required for successful access. The vulnerability's impact is particularly severe because it allows unauthenticated remote attackers to gain access to the FTP server functionality, potentially enabling them to upload malicious files, download sensitive configuration data, or modify system files. The attack vector involves network-level access to the management interface, making it accessible to adversaries who can reach the device's network perimeter.
From an operational perspective, this vulnerability creates significant risk for organizations utilizing Cisco WSA appliances, as it provides a pathway for remote attackers to gain unauthorized access to critical security infrastructure. The fact that the device is only vulnerable when FTP is enabled on the management interface means that administrators must be vigilant about their configuration practices, though the default disabling of this feature provides some protection. However, when FTP is enabled, the vulnerability becomes a serious concern for security posture, as it essentially removes the password requirement for FTP access. The implications extend beyond simple unauthorized access, as attackers who successfully exploit this vulnerability could potentially modify security policies, access logs, or even compromise the entire appliance. This represents a significant escalation from a simple authentication bypass to a full compromise of the security appliance's management capabilities, which could undermine the organization's overall network security strategy.
Organizations should implement immediate mitigation strategies to address this vulnerability, beginning with disabling FTP access on the management interface unless absolutely required for legitimate operational purposes. The recommended approach involves configuring the WSA appliance to disable FTP services on management interfaces while maintaining FTP functionality only on non-management interfaces where it is truly needed. Network segmentation and access control measures should be strengthened to limit exposure of management interfaces to trusted networks only. Additionally, administrators should conduct thorough audits of their WSA configurations to identify any instances where FTP has been enabled on management interfaces, as this represents a direct exposure to the vulnerability. The mitigation strategy should also include monitoring for unauthorized FTP access attempts and implementing network-based intrusion detection systems to identify potential exploitation attempts. Regular security assessments and vulnerability scanning should be performed to ensure that no other configuration weaknesses exist that could compound the risk of exploitation, as this vulnerability could potentially be leveraged as a stepping stone to compromise other systems within the network. The ATT&CK framework categorizes this vulnerability under privilege escalation and credential access tactics, where attackers can leverage the authentication bypass to gain elevated privileges and access sensitive information within the security infrastructure.