CVE-2020-5505 in Freelancy
Summary
by MITRE
Freelancy v1.0.0 allows remote command execution via the "file":"data:application/x-php;base64 substring (in conjunction with "type":"application/x-php"} to the /api/files/ URI.
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Analysis
by VulDB Data Team • 03/21/2024
The vulnerability identified as CVE-2020-5505 affects Freelancy version 1.0.0 and represents a critical remote command execution flaw that enables attackers to execute arbitrary code on the affected system. This vulnerability resides within the file upload functionality of the application's API endpoint at /api/files/, where the system fails to properly validate or sanitize user-supplied file data. The specific technical mechanism involves the exploitation of a base64 encoded PHP payload that is embedded within a data URI scheme, specifically using the "data:application/x-php;base64" substring in conjunction with the "type":"application/x-php" parameter. This allows malicious actors to bypass normal file validation checks and directly inject executable PHP code into the target system.
The technical implementation of this vulnerability stems from inadequate input validation and sanitization within the file handling mechanism of the Freelancy application. When the system processes file uploads through the /api/files/ endpoint, it does not sufficiently verify the content type or actual file contents of uploaded files. The attacker can craft a malicious request that includes a base64 encoded PHP payload within a data URI structure, which the application then processes without proper security checks. This flaw aligns with CWE-434, which describes insecure file upload vulnerabilities where applications accept files from untrusted sources without proper validation. The vulnerability enables attackers to execute commands on the underlying system with the privileges of the web application user, potentially leading to complete system compromise.
The operational impact of CVE-2020-5505 is severe and far-reaching, as it provides attackers with full remote command execution capabilities on the affected server. This vulnerability can be exploited by unauthorized users to gain persistent access to the system, potentially leading to data breaches, system infiltration, and further lateral movement within the network. The attack surface is particularly concerning because it allows remote exploitation without requiring authentication, making it accessible to anyone who can reach the vulnerable API endpoint. The vulnerability's classification under the MITRE ATT&CK framework would fall under T1059.007 for Command and Scripting Interpreter and T1078 for Valid Accounts, as attackers can leverage this vulnerability to execute commands and potentially establish persistent access. The impact extends beyond immediate code execution to include potential data exfiltration, system reconnaissance, and privilege escalation opportunities.
Mitigation strategies for CVE-2020-5505 should focus on implementing robust input validation, content type checking, and proper file handling mechanisms within the application. Organizations should immediately upgrade to a patched version of Freelancy if available, as this vulnerability was likely addressed in subsequent releases. The recommended approach involves implementing strict file type validation that rejects any file attempts to upload with PHP or other potentially executable content types. Additionally, the system should employ proper sanitization of file names and content, ensure that uploaded files are stored outside the web root directory, and implement proper access controls for file operations. Network-level mitigations such as firewall rules restricting access to the vulnerable API endpoint and web application firewalls that can detect and block malicious data URI patterns should also be considered. The implementation of these security controls aligns with the principle of least privilege and defense in depth strategies, which are fundamental to modern cybersecurity practices and help prevent similar vulnerabilities from being exploited in other applications.