CVE-2013-4669 in FortiClient
Summary
by MITRE
FortiClient before 4.3.5.472 on Windows, before 4.0.3.134 on Mac OS X, and before 4.0 on Android; FortiClient Lite before 4.3.4.461 on Windows; FortiClient Lite 2.0 through 2.0.0223 on Android; and FortiClient SSL VPN before 4.0.2258 on Linux proceed with an SSL session after determining that the server s X.509 certificate is invalid, which allows man-in-the-middle attackers to obtain sensitive information by leveraging a password transmission that occurs before the user warning about the certificate problem.
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Analysis
by VulDB Data Team • 05/06/2018
The vulnerability identified as CVE-2013-4669 represents a critical security flaw in FortiClient VPN software across multiple platforms including Windows, macOS, Android, and Linux operating systems. This issue stems from improper certificate validation mechanisms within the SSL/TLS handshake process, where the client application continues to establish a secure session even when it detects that the server's X.509 certificate is invalid or untrusted. The vulnerability affects various versions of FortiClient including the full client, Lite versions, and SSL VPN components, with specific version thresholds indicating the scope of affected releases. The flaw essentially undermines the fundamental security principle of certificate validation that prevents unauthorized parties from impersonating legitimate servers during network communications.
The technical implementation of this vulnerability occurs during the SSL session establishment phase where FortiClient fails to properly enforce certificate validation checks before proceeding with the connection. When the client encounters an invalid certificate, it should terminate the connection attempt and alert the user to the security risk. However, in affected versions, the software continues the SSL negotiation process, allowing the connection to proceed despite the certificate validation failure. This behavior creates a window of opportunity for man-in-the-middle attackers who can intercept and potentially manipulate network traffic between the client and server. The vulnerability is particularly dangerous because it occurs during the initial authentication phase, where users typically enter their credentials, making it possible for attackers to capture sensitive authentication information through password transmission that happens before the user receives any warning about the certificate problem.
The operational impact of this vulnerability extends beyond simple credential theft to encompass broader security implications for organizations relying on FortiClient for secure remote access. Attackers can exploit this weakness to establish unauthorized connections to corporate networks, potentially gaining access to sensitive data, internal systems, and network resources. The vulnerability affects not only individual user sessions but also organizational security policies that depend on proper SSL certificate validation to maintain trust in network communications. Given that FortiClient is commonly deployed for remote access solutions, this flaw could enable attackers to bypass critical security controls designed to prevent unauthorized network access. The risk is amplified when considering that users may not be aware of the compromised connection until after sensitive information has already been transmitted, making detection and mitigation challenging for security administrators.
Organizations should implement immediate remediation measures by upgrading to patched versions of FortiClient software across all affected platforms, with particular attention to the specific version thresholds mentioned in the vulnerability description. The recommended approach includes deploying the latest available versions of FortiClient that have addressed the certificate validation issues, ensuring that all Windows, macOS, Android, and Linux systems are updated to prevent exploitation. Additionally, network administrators should consider implementing additional security monitoring to detect potential exploitation attempts, including unusual authentication patterns or unauthorized network access attempts. The vulnerability aligns with CWE-295 which addresses improper certificate validation, and represents a significant concern from an ATT&CK perspective under the initial access and credential access domains, as it enables adversaries to obtain credentials through man-in-the-middle attacks that bypass standard security controls. Organizations should also review their security policies to ensure proper certificate management practices are in place, including regular certificate validation procedures and user education regarding security warnings during network connections.