CVE-2016-7791 in Exponent
Summary
by MITRE
Exponent CMS 2.3.9 suffers from a remote code execution vulnerability in /install/index.php. An attacker can upload an evil 'exploit.tar.gz' file to the website, then extract it by visiting '/install/index.php?install_sample=../../files/exploit', which leads to arbitrary code execution.
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Analysis
by VulDB Data Team • 05/06/2020
The vulnerability identified as CVE-2016-7791 represents a critical remote code execution flaw within Exponent CMS version 2.3.9 that stems from improper input validation and insecure file handling practices. This vulnerability exists in the installation component of the content management system at the path /install/index.php, where the application fails to properly validate or sanitize file uploads, creating an avenue for malicious actors to execute arbitrary code on the target system. The flaw is particularly concerning as it allows attackers to bypass normal security controls and gain full command execution privileges.
The technical implementation of this vulnerability relies on a combination of insecure file upload mechanisms and directory traversal vulnerabilities. Attackers can craft a malicious exploit.tar.gz file containing malicious code and upload it to the vulnerable system through the installation interface. The vulnerability is exploited by leveraging the install_sample parameter in the URL which accepts a relative path traversal attack. When the attacker visits the specific URL pattern /install/index.php?install_sample=../../files/exploit, the system attempts to extract and process the malicious archive in a location outside the intended directory structure, resulting in code execution. This represents a classic directory traversal vulnerability that allows attackers to manipulate file paths and execute code in unintended locations.
The operational impact of this vulnerability extends far beyond simple code execution, as it provides attackers with complete control over the compromised system. Once executed, the malicious code can be used to establish persistent backdoors, escalate privileges, steal sensitive data, or use the compromised server as a launch point for further attacks against the internal network. The vulnerability affects the entire Exponent CMS installation and can be exploited remotely without requiring authentication, making it particularly dangerous for web applications that are publicly accessible. The attack chain is relatively straightforward and does not require advanced exploitation techniques, which increases the likelihood of successful compromise.
From a cybersecurity perspective, this vulnerability aligns with CWE-22 (Improper Limitation of a Pathname to a Restricted Directory) and CWE-74 (Improper Neutralization of Special Elements in Output Used by a Downstream Component) while mapping to ATT&CK technique T1059.001 (Command and Scripting Interpreter: PowerShell) and T1078 (Valid Accounts) in the context of privilege escalation. Organizations running Exponent CMS 2.3.9 are at significant risk as this vulnerability can be exploited by automated scanners and malicious actors without requiring specialized knowledge or access credentials. The vulnerability demonstrates poor secure coding practices including lack of proper input validation, insufficient access controls, and inadequate file handling procedures that are commonly addressed by security frameworks such as the OWASP Top 10 and NIST Cybersecurity Framework.
Mitigation strategies for CVE-2016-7791 should include immediate patching of the Exponent CMS to a version that addresses the insecure file handling and directory traversal issues. Organizations should implement network-level restrictions to prevent access to the vulnerable installation interface, disable unnecessary file upload capabilities, and deploy web application firewalls to detect and block malicious requests. Additionally, regular security audits should be conducted to identify similar vulnerabilities in other components of the application stack, and proper input validation should be implemented to prevent path traversal attacks. System administrators should also consider implementing monitoring solutions that can detect unusual file upload activities and execution patterns that may indicate exploitation attempts. The vulnerability serves as a reminder of the critical importance of secure file handling and proper access controls in web applications, particularly in content management systems that provide installation and configuration interfaces.