CVE-2017-14186 in FortiOS
Summary
by MITRE
A Cross-site Scripting (XSS) vulnerability in Fortinet FortiOS 5.6.0 to 5.6.2, 5.4.0 to 5.4.6, 5.2.0 to 5.2.12, 5.0 and below versions under SSL VPN web portal allows an authenticated user to inject arbitrary web script or HTML in the context of the victim's browser via the login redir parameter. An URL Redirection attack may also be feasible by injecting an external URL via the affected parameter.
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Analysis
by VulDB Data Team • 01/25/2021
This cross-site scripting vulnerability exists within Fortinet FortiOS SSL VPN web portal implementations across multiple affected versions including 5.6.0 to 5.6.2, 5.4.0 to 5.4.6, 5.2.0 to 5.2.12, and versions 5.0 and below. The flaw specifically manifests in the login redir parameter handling within the SSL VPN web interface, allowing authenticated users to inject malicious web scripts or HTML content that executes in the context of victim browsers. This represents a critical security weakness that directly violates the principles of input validation and output encoding as outlined in CWE-79 Cross-site Scripting. The vulnerability stems from insufficient sanitization of user-supplied input in the redir parameter, which is typically used for redirecting users after successful authentication.
The operational impact of this vulnerability extends beyond simple script injection to include potential URL redirection attacks that could compromise user sessions and facilitate further exploitation. An authenticated attacker with access to the SSL VPN portal can craft malicious URLs containing script payloads that will execute when victims click on links or navigate through the portal. This creates a significant risk for man-in-the-middle attacks and session hijacking scenarios where attackers could redirect users to malicious domains or inject malicious content that persists across user sessions. The vulnerability aligns with ATT&CK technique T1566.001 for Initial Access through spearphishing attachments and T1071.004 for Application Layer Protocol using SSL/TLS, as it enables attackers to manipulate web portal behavior and potentially escalate privileges through session manipulation.
The technical exploitation requires an authenticated user context, making this a privilege escalation vulnerability that could be leveraged by insiders or attackers who have gained initial access through other means. The injection occurs in the login redir parameter, which suggests that the application fails to properly validate or escape user input before incorporating it into web responses. This vulnerability directly impacts the integrity of the web application's response handling and violates fundamental security principles of input validation and output encoding. Organizations using affected FortiOS versions face significant risk of credential theft, session hijacking, and potential lateral movement within their networks. The vulnerability demonstrates poor input validation practices that should be addressed through comprehensive sanitization of all user-supplied data before it is processed or rendered in web responses. Mitigation strategies should include immediate patching to supported FortiOS versions, implementation of web application firewalls, and comprehensive input validation controls that prevent script injection attempts.
Organizations should also implement network segmentation to limit access to SSL VPN portals, enforce strict access controls, and monitor for suspicious URL redirection patterns. The vulnerability highlights the importance of secure coding practices and proper input validation in web applications, particularly in authentication and session management components. Security teams must ensure that all user-supplied parameters are properly sanitized and validated before being incorporated into web responses. This vulnerability serves as a reminder of the critical importance of regular security assessments and patch management processes, as well as the need for comprehensive security training for developers working on web application components. The affected versions represent a significant security gap that required immediate remediation through official Fortinet patches and security updates to prevent exploitation by malicious actors.