CVE-2023-36639 in FortiOS
Summary
by MITRE • 12/13/2023
A use of externally-controlled format string in Fortinet FortiProxy versions 7.2.0 through 7.2.4, 7.0.0 through 7.0.10, FortiOS versions 7.4.0, 7.2.0 through 7.2.4, 7.0.0 through 7.0.11, 6.4.0 through 6.4.12, 6.2.0 through 6.2.15, 6.0.0 through 6.0.17, FortiPAM versions 1.0.0 through 1.0.3 allows attacker to execute unauthorized code or commands via specially crafted API requests.
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Analysis
by VulDB Data Team • 01/02/2024
This vulnerability represents a critical format string injection flaw in Fortinet's FortiProxy and FortiOS products that affects multiple version ranges across different product lines. The issue stems from improper input validation within the API request handling mechanism where externally controlled user input is directly used in format string functions without adequate sanitization or escaping. This vulnerability falls under the CWE-134 category of "Use of Externally-Controlled Format String" which is a well-documented weakness that has been exploited in numerous security incidents across various platforms and applications. The flaw exists in the way the software processes API requests, specifically when parsing user-supplied data that gets interpreted as format specifiers rather than literal values.
The operational impact of this vulnerability is severe as it allows remote attackers to execute arbitrary code or commands on affected systems without authentication. Attackers can craft specially formatted API requests that manipulate the format string parsing logic to inject malicious payloads, potentially leading to complete system compromise. This vulnerability is particularly dangerous because it affects multiple Fortinet products including FortiProxy, FortiOS, and FortiPAM, spanning several major version releases and multiple years of development. The attack surface is broad due to the widespread deployment of Fortinet products in enterprise environments, making this a high-priority target for threat actors seeking persistent access to network infrastructure.
The technical exploitation of this vulnerability requires understanding that format string functions like printf, sprintf, or similar operations are being called with user-controlled input as format specifiers. When an attacker can control the format string itself, they can leverage format specifiers such as %s, %d, %x, or %n to read memory locations, overwrite critical memory addresses, or execute arbitrary code. This type of vulnerability is classified under the ATT&CK technique T1059.001 for Command and Scripting Interpreter and T1078.004 for Valid Accounts, as it enables attackers to execute commands with system privileges and potentially escalate their access. The vulnerability exists in the API processing layer where authentication checks may be bypassed or circumvented, allowing unauthenticated remote code execution.
Organizations should implement immediate mitigations including applying the latest Fortinet security patches released for affected versions, implementing network segmentation to limit API access, and deploying intrusion detection systems to monitor for suspicious API requests. The vulnerability demonstrates the importance of proper input validation and the principle of least privilege in API design. Security teams should also consider implementing API request rate limiting and monitoring for unusual format string patterns in logs. This vulnerability highlights the critical need for secure coding practices and proper validation of all user inputs, particularly in applications that handle external API communications. The impact extends beyond immediate code execution to potential data breaches, system compromise, and disruption of critical network services that organizations rely upon for business continuity.