CVE-2021-24663 in Simple Schools Staff Directory Plugin
Summary
by MITRE • 09/20/2021
The Simple Schools Staff Directory WordPress plugin through 1.1 does not validate uploaded logo pictures to ensure that are indeed images, allowing high privilege users such as admin to upload arbitrary file like PHP, leading to RCE
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Analysis
by VulDB Data Team • 09/22/2021
The vulnerability identified as CVE-2021-24663 affects the Simple Schools Staff Directory WordPress plugin version 1.1 and earlier, presenting a critical security flaw that stems from inadequate input validation during file upload operations. This issue specifically targets the plugin's handling of logo uploads, where the system fails to properly validate file types before accepting and storing user-uploaded content. The vulnerability exists within the plugin's administrative interface, where high-privilege users including administrators possess the ability to bypass essential security checks that should prevent the upload of non-image files. This weakness creates a direct pathway for privilege escalation and remote code execution attacks, as malicious actors can upload PHP files or other executable content that will be processed by the web server.
The technical implementation of this vulnerability resides in the plugin's file validation logic, which does not perform proper MIME type checking or file extension validation for uploaded images. According to CWE-434, this represents a weakness where web applications fail to validate or incorrectly validate file uploads, allowing potentially malicious files to be stored and executed on the server. The flaw directly enables attackers with administrator privileges to upload arbitrary files, including PHP shell scripts, web shells, or other malicious executables that can be accessed through the web server. This vulnerability aligns with ATT&CK technique T1505.003, which describes the use of web shells for maintaining persistent access to compromised systems.
The operational impact of CVE-2021-24663 extends beyond simple privilege escalation, as it enables full remote code execution capabilities that can compromise entire WordPress installations. Once an attacker successfully uploads a malicious file, they can execute arbitrary commands on the server, potentially leading to data exfiltration, lateral movement within the network, or complete system compromise. The vulnerability is particularly dangerous because it requires minimal privileges to exploit, as administrators typically have the necessary permissions to upload logos and other visual elements. This creates a significant risk for educational institutions and organizations using the Simple Schools Staff Directory plugin, as the attack surface is expanded through the administrative interface where legitimate users expect to upload only image files.
Mitigation strategies for this vulnerability should include immediate patching of the Simple Schools Staff Directory plugin to version 1.2 or later, which addresses the file validation issue. Organizations should also implement additional security measures such as restricting file upload capabilities to only allow specific image formats, implementing proper MIME type validation, and configuring web server restrictions to prevent execution of uploaded files in web-accessible directories. The principle of least privilege should be enforced by limiting administrative capabilities to only those users who absolutely require them, and implementing file integrity monitoring to detect unauthorized uploads. Additionally, organizations should consider implementing web application firewalls to detect and block suspicious file upload patterns, and conduct regular security audits to identify similar validation weaknesses in other plugins or custom code components.