CVE-2018-13383 in FortiOS
Summary
by MITRE
A heap buffer overflow in Fortinet FortiOS all versions below 6.0.5 in the SSL VPN web portal may cause the SSL VPN web service termination for logged in users due to a failure to properly handle javascript href data when proxying webpages.
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Analysis
by VulDB Data Team • 10/23/2024
The heap buffer overflow vulnerability identified as CVE-2018-13383 affects Fortinet FortiOS versions prior to 6.0.5 within the SSL VPN web portal functionality. This vulnerability represents a critical security flaw that stems from improper handling of javascript href data during web proxy operations, creating a potential pathway for service disruption and unauthorized access. The vulnerability exists in the SSL VPN web portal component that processes and proxies web content for authenticated users, making it particularly dangerous in enterprise environments where remote access is extensively utilized.
The technical implementation flaw manifests when the SSL VPN web portal processes javascript href attributes in web content that is being proxied through the FortiOS system. The system fails to properly validate or sanitize the length and content of javascript href data, leading to a heap buffer overflow condition. This occurs because the application allocates a fixed-size buffer in memory to handle javascript href data but does not adequately check if incoming data exceeds the allocated buffer boundaries. When malicious or malformed javascript href content is processed, it overflows the allocated heap memory space, potentially causing memory corruption that leads to application instability and service termination.
The operational impact of this vulnerability extends beyond simple service disruption to encompass potential security implications for organizations relying on FortiOS SSL VPN services. When the heap buffer overflow occurs, the SSL VPN web service terminates for logged-in users, effectively cutting off remote access to corporate resources and disrupting business operations. This creates a denial of service condition that can affect productivity and potentially expose sensitive data if users are forced to reconnect or if the service disruption coincides with critical business operations. The vulnerability affects all FortiOS versions below 6.0.5, indicating a widespread exposure across multiple generations of the FortiOS platform.
Organizations should implement immediate mitigations including upgrading to FortiOS version 6.0.5 or later, which contains the necessary patches to address the heap buffer overflow condition. Additionally, network administrators should consider implementing additional monitoring and logging around SSL VPN web portal activities to detect anomalous javascript href data patterns that might indicate exploitation attempts. The vulnerability aligns with CWE-121, heap-based buffer overflow, and represents a specific implementation weakness in the SSL VPN proxy handling logic that violates secure coding practices. From an ATT&CK perspective, this vulnerability could be leveraged in initial access or privilege escalation phases, particularly in environments where SSL VPN is used as a primary remote access mechanism for privileged users.