CVE-2017-6090 in phpCollab
Summary
by MITRE
Unrestricted file upload vulnerability in clients/editclient.php in PhpCollab 2.5.1 and earlier allows remote authenticated users to execute arbitrary code by uploading a file with an executable extension, then accessing it via a direct request to the file in logos_clients/.
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Analysis
by VulDB Data Team • 08/03/2025
The vulnerability identified as CVE-2017-6090 represents a critical unrestricted file upload flaw within the PhpCollab 2.5.1 web application, specifically affecting the clients/editclient.php component. This vulnerability resides in the client management functionality where the application fails to properly validate or sanitize file uploads, creating a pathway for malicious actors to bypass security controls. The flaw is particularly dangerous because it affects authenticated users, meaning that an attacker must first gain valid credentials, but once inside the system, they can leverage this vulnerability to execute arbitrary code on the server. The vulnerability is classified under CWE-434 which specifically addresses the insecure upload of code, making it a direct descendant of well-known software security weaknesses that have plagued web applications for decades. The attack vector requires a user to upload a file with an executable extension such as .php, .asp, or .jsp, which then gets stored in the logos_clients/ directory where it can be accessed directly through a web request, effectively allowing code execution.
The technical implementation of this vulnerability stems from inadequate input validation and insufficient file type checking mechanisms within the file upload functionality. When users upload files through the editclient.php script, the application does not properly verify the file extensions, MIME types, or file contents against a whitelist of acceptable formats. This lack of proper validation allows attackers to upload malicious files that contain executable code, bypassing any server-side security checks that should normally prevent such uploads. The vulnerability is particularly insidious because it leverages the legitimate file upload functionality of the application, making it harder to detect through traditional security monitoring approaches. The stored files are placed in the logos_clients/ directory, which is accessible via the web server, creating a direct path for code execution when the malicious file is accessed through a web browser or automated tooling.
The operational impact of CVE-2017-6090 extends far beyond simple unauthorized file access, as it provides attackers with a persistent foothold within the target environment. Successful exploitation allows for complete system compromise through the execution of arbitrary code, potentially enabling attackers to install backdoors, exfiltrate sensitive data, or use the compromised server as a launchpad for further attacks against internal networks. The vulnerability can be exploited to gain shell access, deploy web shells, or execute malicious payloads that can persist across system reboots. Given that this affects PhpCollab 2.5.1 and earlier versions, organizations using these vulnerable systems face significant risk, particularly in environments where the application handles sensitive client data or serves as a collaboration platform for business-critical operations. The attack scenario aligns with ATT&CK technique T1190 which describes the use of web shell deployment as a method for maintaining persistent access to compromised systems.
Mitigation strategies for CVE-2017-6090 must address both immediate remediation and long-term security improvements. Organizations should immediately upgrade to PhpCollab versions 2.5.2 or later where this vulnerability has been patched, as the official release includes proper input validation and file type checking mechanisms. Additionally, implementing proper file upload restrictions such as MIME type validation, file extension whitelisting, and content-based file analysis can prevent similar vulnerabilities from occurring in other applications. The security controls should include disabling the execution of uploaded files in web-accessible directories, implementing proper file permissions, and conducting regular security audits of file upload functionalities. Organizations should also consider implementing web application firewalls to detect and block suspicious file upload patterns, and establish monitoring procedures to detect unauthorized file uploads or access to uploaded files. The remediation process should also include user access controls, ensuring that only authorized personnel have the ability to upload files to sensitive directories, and regular security training to prevent social engineering attacks that might lead to credential compromise.