CVE-2017-3133 in FortiOS
Summary
by MITRE
A Cross-Site Scripting vulnerability in Fortinet FortiOS versions 5.6.0 and earlier allows attackers to execute unauthorized code or commands via the Replacement Message HTML for SSL-VPN.
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Analysis
by VulDB Data Team • 09/06/2024
The vulnerability identified as CVE-2017-3133 represents a critical cross-site scripting flaw within Fortinet FortiOS software versions 5.6.0 and earlier. This security weakness specifically affects the SSL-VPN functionality of the Fortigate firewall and secure access platform, creating a dangerous attack surface that could be exploited by malicious actors to gain unauthorized access to network resources. The vulnerability stems from inadequate input validation and output encoding mechanisms within the web interface components responsible for handling replacement message HTML content used in SSL-VPN sessions.
The technical implementation of this flaw occurs when the system fails to properly sanitize user-supplied HTML content within the replacement message functionality. Attackers can craft malicious HTML payloads that are then executed in the context of a victim's browser session, bypassing normal security controls and potentially allowing for complete session hijacking or unauthorized command execution. This vulnerability operates at the application layer and leverages the trust relationship between the SSL-VPN client and server, making it particularly dangerous in enterprise environments where privileged access is granted through these secure connections. The flaw aligns with CWE-79 which specifically addresses cross-site scripting vulnerabilities, and represents a classic example of unsafe input handling that enables malicious code injection.
The operational impact of CVE-2017-3133 extends far beyond simple data theft, as successful exploitation could enable attackers to establish persistent access to corporate networks through compromised SSL-VPN sessions. This vulnerability directly enables techniques categorized under the ATT&CK framework's T1071.004 tactic for application layer protocol usage, specifically targeting web application protocols. Organizations using affected FortiOS versions face significant risk of credential theft, data exfiltration, and lateral movement within their networks. The vulnerability's exploitation could result in complete compromise of the SSL-VPN infrastructure, potentially allowing attackers to bypass network segmentation controls and access sensitive internal systems. Given that SSL-VPN services are commonly used for remote access by employees and partners, this flaw creates an attractive attack vector for adversaries seeking to establish footholds within enterprise environments.
Mitigation strategies for CVE-2017-3133 should prioritize immediate implementation of Fortinet's official security patches and firmware updates, as these address the root cause of the vulnerability through proper input sanitization and output encoding mechanisms. Network administrators should also implement additional protective measures including disabling unnecessary SSL-VPN features, implementing strict input validation policies, and monitoring for suspicious HTML content within web interface components. Organizations should consider implementing web application firewalls to detect and block malicious payloads attempting to exploit this vulnerability, while also conducting comprehensive security assessments of their SSL-VPN configurations. The remediation process must include thorough testing of updated firmware to ensure compatibility with existing network infrastructure, as well as comprehensive user training to recognize potential social engineering attempts that might accompany exploitation attempts. Security teams should also establish monitoring procedures to detect unauthorized modifications to replacement message HTML content and maintain detailed audit logs of all SSL-VPN administrative activities.