CVE-2018-16786 in DeDeCMS
Summary
by MITRE
DedeCMS 5.7 SP2 allows XSS via an onhashchange attribute in the msg parameter to /plus/feedback_ajax.php.
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Analysis
by VulDB Data Team • 03/26/2020
DedeCMS 5.7 SP2 contains a cross-site scripting vulnerability that arises from insufficient input validation of the msg parameter in the /plus/feedback_ajax.php endpoint. This vulnerability specifically exploits the onhashchange attribute, which represents a critical security flaw in the application's handling of user-supplied data. The flaw enables attackers to inject malicious javascript code that executes in the context of other users' browsers, making it a severe threat to the application's security posture. The vulnerability falls under the CWE-79 category of Cross-Site Scripting, which is classified as a common weakness in web applications that fail to properly sanitize user input. This particular instance represents a reflected XSS attack vector where malicious payloads are injected through the feedback form functionality and executed when other users view the affected content.
The technical exploitation of this vulnerability occurs when an attacker crafts a malicious payload containing the onhashchange attribute within the msg parameter of the feedback_ajax.php endpoint. When the application processes this input without proper sanitization or encoding, the malicious javascript code gets embedded into the page's HTML structure. The onhashchange event handler creates a specific attack surface because it executes javascript code whenever the browser's URL hash changes, providing attackers with persistent execution capabilities. This particular attack vector leverages the application's failure to implement proper output encoding for dynamic content, allowing attackers to bypass security controls that might otherwise prevent such injections. The vulnerability demonstrates a fundamental flaw in the application's data validation and sanitization processes, where user input flows directly into the application's output without adequate security filtering.
The operational impact of this vulnerability extends beyond simple data theft or session hijacking, as it provides attackers with the capability to perform more sophisticated attacks against users of the vulnerable DedeCMS installation. Successful exploitation could enable attackers to steal session cookies, perform unauthorized actions on behalf of users, redirect them to malicious websites, or even execute more advanced attacks such as credential theft through keylogging or form grabbing. The reflected nature of this XSS vulnerability means that attackers can craft specific URLs that, when clicked by victims, automatically execute malicious code without requiring any additional user interaction beyond visiting the compromised page. This makes the vulnerability particularly dangerous in environments where users may click on links in emails, forums, or other web-based communication channels. The attack surface is further expanded by the fact that this vulnerability affects the feedback functionality, which is commonly used and accessible to all users, potentially allowing attackers to reach a wide audience within the application's user base.
Mitigation strategies for this vulnerability must address both immediate remediation and long-term security improvements in the application's codebase. The primary fix involves implementing proper input validation and output encoding for all user-supplied data, particularly in the feedback_ajax.php endpoint where the vulnerability originates. The application should sanitize all input parameters, including the msg parameter, by removing or encoding potentially dangerous characters and attributes such as onhashchange, onclick, onmouseover, and other event handlers. Security measures should include implementing Content Security Policy headers to prevent unauthorized script execution, using proper HTML encoding functions when rendering user content, and applying input validation that rejects or sanitizes malicious payloads before they are processed by the application. Organizations should also implement regular security testing including automated vulnerability scanning and manual penetration testing to identify similar issues within the application. The remediation process should follow industry standards such as the OWASP Top Ten security guidelines and incorporate defensive programming practices that prevent similar vulnerabilities from being introduced in future development cycles. Additionally, implementing proper logging and monitoring of user input can help detect and respond to exploitation attempts in real-time.