CVE-2018-13381 in FortiOS
Summary
by MITRE
A buffer overflow vulnerability in Fortinet FortiOS 6.0.0 to 6.0.4, 5.6.0 to 5.6.7, 5.4 and below versions under SSL VPN web portal allows a non-authenticated attacker to perform a Denial-of-service attack via special craft message payloads.
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Analysis
by VulDB Data Team • 09/26/2023
The buffer overflow vulnerability identified as CVE-2018-13381 affects Fortinet FortiOS versions 6.0.0 through 6.0.4, 5.6.0 through 5.6.7, and all versions prior to 5.4 within the SSL VPN web portal component. This vulnerability represents a critical security flaw that can be exploited by unauthenticated attackers to execute denial-of-service attacks against affected FortiOS appliances. The vulnerability specifically manifests when the system processes specially crafted message payloads through the SSL VPN web portal interface, creating a condition where input data exceeds the allocated buffer space and overflows into adjacent memory regions.
The technical implementation of this buffer overflow occurs within the SSL VPN web portal processing logic where insufficient input validation and bounds checking mechanisms fail to properly handle oversized or malformed data packets. When an attacker sends maliciously crafted payloads to the SSL VPN web portal, the system attempts to process these inputs without adequate safeguards, leading to memory corruption that can cause the affected service to crash or become unresponsive. This flaw falls under the Common Weakness Enumeration category CWE-121, which describes stack-based buffer overflow conditions where insufficient bounds checking allows attackers to overwrite adjacent memory locations. The vulnerability demonstrates characteristics consistent with CWE-787, heap-based buffer overflow, when the processing of crafted inputs leads to memory corruption beyond the intended buffer boundaries.
The operational impact of this vulnerability extends beyond simple service disruption to potentially compromise the availability of critical network security infrastructure. Organizations relying on Fortinet FortiOS appliances for remote access and SSL VPN services face significant risk when exposed to this vulnerability, as attackers can exploit it to render the SSL VPN web portal completely inaccessible to legitimate users. The attack requires no authentication credentials, making it particularly dangerous as it can be executed from any network location without prior access to the system. This vulnerability directly impacts the availability component of the CIA triad and can be classified under the MITRE ATT&CK framework's T1499 technique for Network Denial of Service, where adversaries leverage system weaknesses to prevent legitimate users from accessing network resources.
Organizations should implement immediate mitigations including applying the latest Fortinet security patches and firmware updates that address this specific buffer overflow vulnerability. Network segmentation and access controls should be strengthened to limit exposure of vulnerable SSL VPN services to untrusted networks. Additionally, implementing network monitoring solutions that can detect anomalous traffic patterns associated with buffer overflow exploitation attempts provides valuable defensive intelligence. System administrators should also consider disabling SSL VPN web portal functionality if not immediately required, reducing the attack surface until proper patches are deployed. The vulnerability highlights the importance of maintaining current security firmware versions and implementing robust input validation mechanisms across all network services to prevent similar buffer overflow conditions from compromising system availability and integrity.