CVE-2019-16218 in WordPress
Summary
by MITRE
WordPress before 5.2.3 allows XSS in stored comments.
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Analysis
by VulDB Data Team • 12/19/2023
WordPress versions prior to 5.2.3 contained a cross-site scripting vulnerability in the comment handling system that allowed attackers to inject malicious scripts into stored comments. This vulnerability specifically affected the comment processing pipeline where user input was not properly sanitized before being stored in the database and subsequently rendered on comment display pages. The flaw occurred because the application failed to adequately filter and escape special characters in comment content, particularly when comments contained html tags or javascript code. Attackers could exploit this by submitting comments with malicious payloads that would execute in the browsers of other users who viewed the affected comments. The vulnerability was classified as a stored cross-site scripting flaw under CWE-79 which represents one of the most common and dangerous web application security issues. This type of vulnerability allows attackers to persist their malicious code within the application's database, making it particularly dangerous as the payload executes every time the affected content is displayed. The impact of this vulnerability extended beyond simple script execution, as it could potentially be leveraged for session hijacking, credential theft, or redirection to malicious websites. According to ATT&CK framework category TA0001, this vulnerability falls under the initial access phase where adversaries establish a foothold through user interaction with malicious content. The vulnerability was particularly concerning in WordPress environments where users could post comments on blogs, news sites, or other content management systems that relied on user-generated content. The attack vector required minimal privileges as any registered user could submit comments, making it an attractive target for malicious actors seeking to compromise other users. The security patch released with WordPress 5.2.3 addressed this issue by implementing stricter input validation and output escaping mechanisms for comment content. This fix aligned with industry best practices for preventing XSS vulnerabilities and demonstrated the importance of proper data sanitization in web applications. Organizations running older WordPress versions were strongly advised to upgrade immediately to prevent exploitation of this vulnerability.
The technical implementation of this vulnerability exploited the lack of proper content sanitization in WordPress's comment processing system. When users submitted comments containing html or javascript code, the application failed to strip or escape these potentially dangerous elements before storing them in the database. This oversight meant that when other users viewed the comment section, the malicious code would execute in their browsers as part of the normal page rendering process. The vulnerability was particularly dangerous because it was a stored XSS flaw, meaning the malicious code persisted in the database rather than being executed only during a single request. This characteristic allowed attackers to craft sophisticated payloads that could perform actions such as stealing cookies, redirecting users to phishing sites, or executing additional malicious commands. The vulnerability was consistent with CWE-79 patterns where inadequate input validation and output encoding created opportunities for attackers to inject malicious scripts. Security researchers noted that this vulnerability could be particularly effective in environments where users had elevated privileges or where the comment system was used in conjunction with other web applications. The patch implemented by WordPress developers focused on enhancing the wp_kses function which is responsible for sanitizing html content, ensuring that only safe html tags and attributes were preserved while dangerous elements were properly escaped or removed. This approach aligned with the principle of least privilege and defense in depth, where multiple layers of security controls were implemented to prevent similar vulnerabilities from occurring in the future.
The operational impact of CVE-2019-16218 extended far beyond simple script injection, as it created a persistent threat vector that could be exploited across multiple user sessions. Organizations that relied heavily on user-generated content, such as news portals, blogs, and community forums, faced significant risks when running vulnerable WordPress installations. The vulnerability could be exploited to perform session hijacking attacks, where attackers would steal user authentication tokens and gain unauthorized access to accounts. Additionally, the stored nature of the vulnerability meant that even if the initial exploit was detected and patched, the malicious code remained embedded in the database and could continue to affect users until manually removed. This characteristic made the vulnerability particularly attractive to threat actors seeking long-term access to compromised systems. The attack could be executed through simple comment submissions without requiring special privileges or advanced technical skills, making it accessible to a broad range of malicious actors. Security teams were particularly concerned about the potential for this vulnerability to be used in combination with other attacks, such as credential harvesting or data exfiltration. The vulnerability also highlighted the importance of maintaining up-to-date software, as the patch was readily available but many organizations failed to deploy it promptly. The incident reinforced the need for comprehensive security testing and monitoring of user input handling mechanisms in web applications, particularly those that process and display user-generated content. Organizations were advised to implement additional security measures such as web application firewalls and regular security audits to detect and prevent similar vulnerabilities from being exploited in their environments. The vulnerability served as a reminder of the critical importance of proper input validation and output encoding in preventing cross-site scripting attacks.