CVE-2020-20699 in S-CMS PHP
Summary
by MITRE • 07/30/2021
A cross site scripting (XSS) vulnerability in S-CMS PHP v3.0 allows attackers to execute arbitrary web scripts or HTML via a crafted payload entered into the Copyright text box under Basic Settings.
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Analysis
by VulDB Data Team • 08/06/2021
The vulnerability identified as CVE-2020-20699 represents a critical cross site scripting flaw within S-CMS PHP version 3.0 that exposes the system to persistent malicious code execution. This weakness resides in the Basic Settings section where users can input copyright information, creating an attack vector that allows adversaries to inject malicious scripts directly into the CMS interface. The vulnerability stems from inadequate input validation and output sanitization mechanisms that fail to properly escape or filter user-supplied data before rendering it within the web application's response.
The technical implementation of this XSS vulnerability occurs when malicious input is accepted through the Copyright text box field without proper sanitization measures. When the system displays this information back to users, it renders the injected HTML or JavaScript code directly within the browser context, enabling attackers to execute arbitrary scripts in the victim's browser session. This type of vulnerability falls under CWE-79 which specifically addresses cross-site scripting flaws in web applications, where improper validation of user input leads to code injection that can be executed in the context of other users' browsers.
The operational impact of this vulnerability extends beyond simple script execution as it can enable attackers to perform session hijacking, steal sensitive information, redirect users to malicious websites, or even escalate privileges within the CMS environment. An attacker could craft payloads that steal administrator cookies, modify content, or create backdoors within the system. The persistent nature of this vulnerability means that once exploited, the malicious code will execute every time users view the affected page, potentially affecting all users who access the CMS interface. This vulnerability specifically aligns with ATT&CK technique T1566 which covers social engineering through malicious content delivery, and T1059 which involves execution through command and scripting interpreters.
Mitigation strategies for CVE-2020-20699 should focus on implementing comprehensive input validation and output encoding mechanisms throughout the application. The most effective approach involves sanitizing all user inputs through proper escaping techniques before rendering them in HTML contexts, implementing Content Security Policy headers to restrict script execution, and utilizing parameterized queries or prepared statements for any dynamic content generation. Additionally, administrators should immediately upgrade to patched versions of S-CMS PHP, disable unnecessary user input fields where possible, and implement proper access controls to limit who can modify CMS settings. Regular security audits and input validation testing should be conducted to prevent similar vulnerabilities from emerging in other parts of the application, as this flaw demonstrates the critical importance of proper data sanitization in web applications. The vulnerability highlights the necessity of following secure coding practices and adhering to OWASP Top Ten security guidelines to prevent such persistent threats in content management systems.