CVE-2016-3978 in FortiOS
Summary
by MITRE
The Web User Interface (WebUI) in FortiOS 5.0.x before 5.0.13, 5.2.x before 5.2.3, and 5.4.x before 5.4.0 allows remote attackers to redirect users to arbitrary web sites and conduct phishing attacks or cross-site scripting (XSS) attacks via the "redirect" parameter to "login."
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Analysis
by VulDB Data Team • 07/13/2022
The vulnerability identified as CVE-2016-3978 represents a critical security flaw in Fortinet's FortiOS web user interface that affects multiple versions of the firewall operating system. This issue resides within the authentication handling mechanism of the WebUI component, specifically in how the system processes the redirect parameter during login operations. The flaw enables malicious actors to manipulate the redirection behavior of the authentication interface, creating a pathway for various sophisticated attacks that can compromise user sessions and system integrity.
The technical implementation of this vulnerability stems from inadequate input validation and sanitization within the FortiOS WebUI login handler. When users attempt to authenticate through the web interface, the system accepts a redirect parameter that specifies where users should be directed after successful login. However, the application fails to properly validate or sanitize this parameter, allowing attackers to inject malicious URLs or script code. This improper handling of user-supplied input directly maps to CWE-601, which describes open redirect vulnerabilities where applications redirect users to untrusted destinations, and CWE-79, which encompasses cross-site scripting flaws where malicious scripts are injected into web applications.
The operational impact of this vulnerability extends far beyond simple redirection attacks, creating a comprehensive threat vector that can be leveraged for sophisticated phishing campaigns and session hijacking operations. Attackers can craft malicious URLs that appear legitimate to users but redirect them to attacker-controlled domains, effectively enabling credential theft through phishing attacks. Additionally, the vulnerability's susceptibility to cross-site scripting allows for the execution of malicious JavaScript within the context of authenticated user sessions, potentially enabling attackers to escalate privileges, access sensitive configuration data, or perform unauthorized administrative actions. This vulnerability directly aligns with ATT&CK technique T1566 for social engineering through phishing and T1071.001 for application layer protocol usage.
Organizations utilizing affected FortiOS versions face significant operational risks when this vulnerability remains unpatched, as it provides attackers with a low-effort pathway to compromise network security. The attack surface is particularly concerning given that the flaw exists in the authentication interface, which is frequently accessed by legitimate users and administrators. Security teams must recognize that successful exploitation can result in complete administrative control over the affected firewall, potentially allowing attackers to modify security policies, access network traffic, or establish persistent access points within the network infrastructure. The vulnerability's persistence across multiple version lines (5.0.x, 5.2.x, and 5.4.x) indicates a fundamental design flaw that required comprehensive patching across the entire product lineage. Mitigation strategies should include immediate deployment of Fortinet's official patches, implementation of network monitoring for suspicious redirect patterns, and enhanced user awareness training to identify potential phishing attempts. Additionally, organizations should consider implementing additional security controls such as web application firewalls and network segmentation to limit the potential impact of successful exploitation attempts.