CVE-2020-21929 in Eyoucms
Summary
by MITRE • 08/11/2021
A stored cross site scripting (XSS) vulnerability in the web_copyright field of Eyoucms v1.4.1 allows authenticated attackers to execute arbitrary web scripts or HTML.
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Analysis
by VulDB Data Team • 08/16/2021
The vulnerability CVE-2020-21929 represents a critical stored cross site scripting flaw within the Eyoucms content management system version 1.4.1. This security weakness specifically targets the web_copyright field, which serves as a designated input area for copyright information within the CMS interface. The vulnerability arises from insufficient input validation and output sanitization mechanisms that fail to properly escape or filter user-supplied content before storing and subsequently rendering it within web pages. Attackers who have authenticated access to the system can exploit this flaw by injecting malicious javascript code or HTML payloads into the copyright field, which then executes in the context of other users' browsers when they view affected pages.
The technical nature of this vulnerability aligns with CWE-79, which categorizes cross site scripting flaws as weaknesses in web applications that allow attackers to inject client-side scripts into web pages viewed by other users. This particular implementation flaw demonstrates how even seemingly benign input fields can become attack vectors when proper security controls are absent. The stored nature of the vulnerability means that the malicious payload persists in the database and executes automatically whenever affected pages are accessed, making it particularly dangerous as it can affect multiple users without requiring them to interact with the malicious content directly. The authenticated requirement reduces the attack surface but does not eliminate the risk, as compromised accounts or insider threats can leverage this vulnerability effectively.
The operational impact of CVE-2020-21929 extends beyond simple script execution, as it can enable attackers to perform various malicious activities including session hijacking, credential theft, data exfiltration, and redirection to malicious websites. An attacker could inject scripts that steal cookies or session tokens from authenticated users, potentially gaining unauthorized access to administrative panels or user accounts. The vulnerability also enables the execution of malicious actions such as modifying content, deleting data, or creating new user accounts with elevated privileges. Additionally, the stored XSS can be used to deliver malware payloads or phishing content that appears legitimate to users, making it an effective vector for social engineering attacks. The impact is particularly severe in environments where the CMS is used for corporate or government websites where users may have access to sensitive information.
Mitigation strategies for CVE-2020-21929 should focus on implementing robust input validation and output encoding mechanisms for all user-supplied content, particularly in fields that are rendered directly within web pages. The recommended approach includes implementing strict sanitization filters that remove or escape potentially dangerous characters and tags from the web_copyright field input. Organizations should also apply the latest security patches provided by Eyoucms vendors, as this vulnerability was likely addressed in subsequent releases. Additional protective measures include implementing content security policies that restrict script execution, using proper output encoding when rendering user content, and conducting regular security audits of all input fields. The implementation of web application firewalls and security monitoring systems can help detect and prevent exploitation attempts. From a defensive perspective, this vulnerability highlights the importance of following secure coding practices and adhering to the principle of least privilege, ensuring that authenticated users have appropriate access controls and that all input validation occurs at multiple layers within the application architecture. This case study demonstrates how vulnerabilities in content management systems can serve as entry points for more extensive attacks, reinforcing the need for comprehensive security measures across all application components.