CVE-2017-3128 in FortiOS
Summary
by MITRE
A stored XSS (Cross-Site-Scripting) vulnerability in Fortinet FortiOS allows attackers to execute unauthorized code or commands via the policy global-label parameter.
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Analysis
by VulDB Data Team • 10/03/2020
The vulnerability identified as CVE-2017-3128 represents a critical stored cross-site scripting flaw within Fortinet FortiOS software versions 5.4.0 through 5.4.7, 5.2.0 through 5.2.10, and 5.0.0 through 5.0.14. This vulnerability specifically affects the policy global-label parameter handling mechanism, creating a persistent security weakness that can be exploited by remote attackers to execute malicious code within the context of a victim's browser session. The flaw resides in the web-based management interface of FortiOS, which processes user-supplied input without proper sanitization or validation, allowing attackers to inject malicious scripts that persist in the system's database and execute whenever the affected page is accessed.
The technical implementation of this vulnerability stems from insufficient input validation within the FortiOS policy management functionality. When administrators configure security policies, they can assign global labels to identify and organize policy rules. The system fails to properly sanitize or encode user-provided label content before storing it in the database, creating a condition where malicious payloads can be stored and subsequently executed. This stored XSS condition occurs because the application directly incorporates user-supplied data into web pages without appropriate context-dependent encoding or escaping mechanisms. The vulnerability is classified under CWE-79 as a failure to sanitize or incorrectly sanitizing input data, making it particularly dangerous as the malicious code persists across multiple sessions and user interactions.
The operational impact of CVE-2017-3128 extends beyond simple script execution, as attackers can leverage this vulnerability to perform a wide range of malicious activities including session hijacking, data exfiltration, and privilege escalation. An attacker who successfully exploits this vulnerability can inject JavaScript code that can steal administrative credentials, modify security policies, or redirect users to malicious websites. The persistence of the stored payload means that even if administrators attempt to remediate the issue by updating the label content, the original malicious script remains embedded in the database. This vulnerability directly aligns with ATT&CK technique T1059.007 for Command and Scripting Interpreter, where adversaries use web-based interfaces to execute malicious commands. Additionally, the vulnerability enables techniques such as T1566 for Phishing and T1071.001 for Application Layer Protocol, as attackers can craft malicious payloads that redirect users or harvest sensitive information from authenticated sessions.
Mitigation strategies for CVE-2017-3128 require immediate implementation of multiple defensive measures. Organizations should prioritize applying the latest Fortinet security patches and firmware updates that address this vulnerability, as Fortinet released specific fixes for affected versions. Network administrators should implement additional input validation controls at the web application level, including implementing proper HTML entity encoding for all user-supplied input fields, particularly those used for policy labels and descriptions. The implementation of Content Security Policy headers can provide additional protection against script execution, while regular security audits of policy configurations should be conducted to identify and remediate any existing malicious payloads. Organizations should also consider implementing network segmentation and access controls to limit the scope of potential exploitation, ensuring that only authorized personnel have access to the affected administrative interfaces. The vulnerability demonstrates the critical importance of input validation in web applications and highlights the need for comprehensive security testing of administrative interfaces to prevent similar stored XSS conditions from persisting in network security infrastructure components.