CVE-2017-7733 in FortiOS
Summary
by MITRE
A Cross-Site-Scripting (XSS) vulnerability in Fortinet FortiOS 5.4.0 to 5.4.5 and 5.6.0 allows a remote unauthenticated attacker to execute arbitrary javascript code via webUI "Login Disclaimer" redir parameter.
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Analysis
by VulDB Data Team • 01/21/2021
The vulnerability identified as CVE-2017-7733 represents a critical cross-site scripting flaw within Fortinet FortiOS versions 5.4.0 through 5.4.5 and 5.6.0, specifically affecting the web-based management interface. This vulnerability exists in the login disclaimer functionality where the redir parameter is improperly handled, creating an avenue for malicious actors to inject and execute arbitrary javascript code within the context of a victim's browser session. The flaw stems from insufficient input validation and output encoding mechanisms within the web user interface components of the FortiOS operating system, which is widely deployed in enterprise network security appliances including firewalls and unified threat management devices.
The technical exploitation of this vulnerability occurs through manipulation of the redir parameter in the login disclaimer functionality, which allows attackers to craft malicious URLs that, when visited by authenticated users, execute javascript code in their browser context. This represents a classic reflected cross-site scripting attack pattern where the malicious payload is embedded within the URL parameters and executed when the user's browser processes the response from the vulnerable web application. The vulnerability is particularly dangerous because it does not require authentication for initial exploitation, making it accessible to remote attackers who can leverage it to compromise user sessions and potentially gain unauthorized access to network resources. The flaw aligns with CWE-79 which specifically addresses cross-site scripting vulnerabilities, and demonstrates characteristics consistent with ATT&CK technique T1059.007 for script-based execution.
The operational impact of this vulnerability extends beyond simple code execution, as it can enable attackers to perform session hijacking, steal user credentials, manipulate web application functionality, and potentially escalate privileges within the network infrastructure. Network administrators using affected FortiOS versions face significant risk of unauthorized access to their security appliances, which could lead to complete compromise of network defenses. The vulnerability affects the core management interface of FortiOS devices, meaning that successful exploitation could allow attackers to modify security policies, access sensitive configuration data, and potentially redirect network traffic through malicious proxies. Organizations relying on Fortinet appliances for network security are particularly vulnerable since these devices often serve as critical infrastructure components that control network access and security policies.
Mitigation strategies for CVE-2017-7733 should prioritize immediate deployment of Fortinet's official security patches and firmware updates that address the input validation and output encoding deficiencies in the web UI components. Network administrators should implement web application firewalls to filter malicious traffic targeting the vulnerable redir parameter and consider disabling unnecessary web interface functionality when not required for administrative tasks. Additionally, implementing strict input validation controls and output encoding mechanisms within the web application framework can help prevent similar vulnerabilities from occurring in other components of the system. Regular security assessments and vulnerability scanning should be conducted to identify and remediate similar issues within the broader network infrastructure, particularly focusing on the web-based management interfaces of network security appliances. Organizations should also consider implementing network segmentation and access controls to limit the potential impact of successful exploitation attempts.