CVE-2018-1352 in FortiOS
Summary
by MITRE
A format string vulnerability in Fortinet FortiOS 5.6.0 allows attacker to execute unauthorized code or commands via the SSH username variable.
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Analysis
by VulDB Data Team • 05/09/2020
The vulnerability identified as CVE-2018-1352 represents a critical format string vulnerability within Fortinet FortiOS version 5.6.0 that specifically affects the Secure Shell protocol implementation. This flaw resides in how the system processes SSH username variables during authentication procedures, creating an exploitable condition that can be leveraged by remote attackers to gain unauthorized system access. The vulnerability stems from improper input validation and sanitization of user-supplied data within the SSH authentication flow, where the system fails to properly escape or validate format specifiers in the username parameter.
This format string vulnerability operates at the core of the authentication mechanism, where the system's failure to properly handle user-provided input creates opportunities for attackers to inject malicious format specifiers that can be interpreted by the underlying printf-family functions. The exploitation occurs when an attacker crafts a specially formatted username string containing format specifiers such as %s, %x, or %n that can trigger unintended behavior in the application's string processing functions. When the system attempts to process this malformed input, it can lead to memory corruption, information disclosure, or arbitrary code execution depending on the specific implementation details and the attacker's control over the execution flow.
The operational impact of this vulnerability extends beyond simple privilege escalation as it provides attackers with the capability to execute arbitrary commands on the affected FortiOS system with the privileges of the SSH service account. This can result in complete system compromise, data exfiltration, and potential lateral movement within the network infrastructure. The vulnerability affects organizations using Fortinet FortiOS 5.6.0 and potentially other versions in the 5.6.x series, making it a widespread concern for enterprise security deployments that rely on Fortinet's network security appliances for perimeter protection and access control.
Security researchers have categorized this vulnerability under CWE-134, which specifically addresses format string vulnerabilities where format strings are constructed from user-controlled data without proper validation or sanitization. The attack vector aligns with ATT&CK technique T1210, which involves exploitation of remote services to gain access to systems through vulnerabilities in network services. Organizations utilizing Fortinet appliances in their security infrastructure face significant risk as this vulnerability can be exploited without requiring authentication to the system itself, making it particularly dangerous for network security devices that are often exposed to external threats.
Mitigation strategies for CVE-2018-1352 require immediate implementation of Fortinet's security patches and firmware updates that address the specific format string handling issue in the SSH implementation. Organizations should also consider implementing network segmentation and access controls to limit exposure of vulnerable FortiOS systems to untrusted networks. Additional defensive measures include monitoring SSH login attempts for unusual patterns and implementing intrusion detection systems that can identify exploitation attempts targeting this specific vulnerability. The vulnerability highlights the importance of proper input validation and secure coding practices in network security appliances, particularly when handling user-supplied data in authentication mechanisms where the consequences of improper handling can be catastrophic for organizational security posture.