CVE-2020-21865 in ThinkPHP50-CMS
Summary
by MITRE • 10/08/2021
ThinkPHP50-CMS v1.0 contains a remote code execution (RCE) vulnerability in the component /public/?s=captcha.
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Analysis
by VulDB Data Team • 10/10/2021
The vulnerability identified as CVE-2020-21865 represents a critical remote code execution flaw within ThinkPHP50-CMS version 1.0, specifically affecting the captcha component located at /public/?s=captcha. This vulnerability stems from improper input validation and sanitization mechanisms that fail to properly filter user-supplied data before processing. The flaw exists in the application's handling of captcha parameters, which allows malicious actors to inject arbitrary code that gets executed on the target server with the privileges of the web application. Such a vulnerability provides attackers with full control over the affected system, enabling them to execute commands, access sensitive data, and potentially establish persistent access. The issue is particularly concerning as it affects a core component that handles user authentication and verification processes, making it a prime target for exploitation. The vulnerability is classified under CWE-94, which encompasses weaknesses related to the execution of code with elevated privileges, and aligns with ATT&CK technique T1059.007 for command and scripting interpreter. The remote nature of this vulnerability means that attackers can exploit it without requiring physical access to the system, making it highly dangerous for publicly accessible web applications.
The technical exploitation of this vulnerability occurs through the manipulation of the captcha parameter in the URL structure, where user input is directly processed without adequate sanitization. When the application attempts to generate or validate a captcha, the malformed input allows attackers to inject malicious code that gets executed within the context of the web server process. This occurs due to the application's failure to implement proper input validation, output encoding, and secure coding practices. The vulnerability demonstrates poor defensive programming where the system assumes that all input is legitimate and trustworthy, failing to implement proper security controls. Attackers can leverage this weakness to perform arbitrary code execution, potentially leading to complete system compromise. The flaw exists in the application's core architecture where input parameters are not properly validated against known safe patterns or allowed character sets, creating an opening for malicious payload injection. This type of vulnerability is particularly dangerous because it can be exploited through simple HTTP requests, making it accessible to attackers with minimal technical expertise.
The operational impact of CVE-2020-21865 extends beyond immediate system compromise to encompass potential data breaches, service disruption, and regulatory compliance violations. Organizations running affected ThinkPHP50-CMS installations face significant risk of unauthorized access to sensitive information, including user credentials, personal data, and business-critical information stored within the database. The vulnerability can be exploited to establish backdoors, install malware, or perform data exfiltration operations that may go undetected for extended periods. Additionally, the compromise of a single web application can serve as a foothold for lateral movement within network environments, potentially leading to broader system infiltration. The financial implications include potential regulatory fines under data protection laws, legal liabilities, and reputational damage from security incidents. Organizations may also face increased operational costs related to incident response, system remediation, and enhanced security measures. The vulnerability's impact is amplified by the fact that ThinkPHP is widely used, meaning that exploitation could affect numerous organizations simultaneously, creating a broader security threat landscape.
Mitigation strategies for CVE-2020-21865 require immediate action to address the underlying vulnerability through software updates and configuration changes. The primary recommendation involves upgrading to a patched version of ThinkPHP50-CMS that addresses the input validation and sanitization issues. Organizations should also implement network-level protections including web application firewalls and intrusion detection systems that can identify and block malicious requests targeting the vulnerable captcha endpoint. Input validation controls should be strengthened to ensure that all parameters are properly sanitized and validated against expected formats. The principle of least privilege should be enforced by running web applications with minimal required permissions and implementing proper output encoding to prevent code injection. Security monitoring should be enhanced to detect anomalous behavior patterns that may indicate exploitation attempts. Additionally, organizations should conduct comprehensive security assessments of their web applications to identify similar vulnerabilities and implement secure coding practices. Regular security updates and patch management processes should be established to prevent future occurrences of similar vulnerabilities. The implementation of security awareness training for development teams can help prevent such flaws in future application development cycles. Organizations should also consider implementing application-level protections such as content security policies and input/output filtering mechanisms to provide additional layers of defense against exploitation attempts.