CVE-2015-3440 in WordPress
Summary
by MITRE
Cross-site scripting (XSS) vulnerability in wp-includes/wp-db.php in WordPress before 4.2.1 allows remote attackers to inject arbitrary web script or HTML via a long comment that is improperly stored because of limitations on the MySQL TEXT data type.
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Analysis
by VulDB Data Team • 02/06/2025
The CVE-2015-3440 vulnerability represents a critical cross-site scripting flaw discovered in WordPress versions prior to 4.2.1, specifically within the wp-includes/wp-db.php file. This vulnerability arises from improper handling of comment data during database storage operations, creating a pathway for remote attackers to execute malicious scripts in the context of affected websites. The flaw exploits the limitations inherent to MySQL TEXT data types when processing excessively long comment content, allowing attackers to bypass standard input validation mechanisms and inject malicious code that persists in the database.
The technical exploitation of this vulnerability stems from WordPress's inadequate sanitization of comment data before storage, particularly when comments exceed the maximum capacity of MySQL TEXT fields. When a comment surpasses the defined limits, the database truncates or mishandles the data in a manner that preserves malicious payloads within the stored content. This behavior creates a persistent XSS vector because the improperly stored comment data is later rendered on web pages without proper output encoding, enabling attackers to execute scripts in users' browsers. The vulnerability manifests when the system processes long comment strings that exceed MySQL TEXT field limitations, causing the system to store malformed data that contains executable JavaScript code.
The operational impact of CVE-2015-3440 extends beyond simple script injection, as it can enable attackers to perform a wide range of malicious activities including session hijacking, credential theft, defacement of websites, and redirection to malicious domains. The persistent nature of the vulnerability means that once exploited, the injected scripts remain active until the affected WordPress installation is updated, potentially compromising all users who view the malicious comment. Attackers can leverage this vulnerability to gain unauthorized access to user accounts, manipulate website content, and potentially use the compromised site as a launching point for further attacks within a network. The vulnerability particularly affects WordPress installations that handle user-generated content extensively, making it a significant concern for blogs, forums, and content management systems relying on comment functionality.
Security mitigations for CVE-2015-3440 primarily focus on updating to WordPress version 4.2.1 or later, which includes proper input validation and sanitization of comment data. Organizations should implement comprehensive input validation at multiple layers, including database storage operations, to prevent oversized data from being improperly stored. The implementation of proper output encoding and content security policies can provide additional protection against XSS exploitation. According to CWE standards, this vulnerability relates to CWE-79, which addresses cross-site scripting flaws, while ATT&CK framework references this as part of the web application attack surface where adversaries can leverage input validation weaknesses to execute malicious code. Regular security audits of database storage operations and input handling mechanisms should be conducted to identify similar vulnerabilities that may exist in custom plugins or themes, as this flaw demonstrates the importance of proper data type handling and validation throughout the application lifecycle.