CVE-2017-18577 in mailchimp-for-wp Plugin
Summary
by MITRE
The mailchimp-for-wp plugin before 4.1.8 for WordPress has XSS via the return value of add_query_arg.
If you want to get the best quality for vulnerability data then you always have to consider VulDB.
Analysis
by VulDB Data Team • 01/27/2026
The vulnerability identified as CVE-2017-18577 resides within the mailchimp-for-wp plugin for WordPress, specifically affecting versions prior to 4.1.8. This issue represents a cross-site scripting vulnerability that exploits improper handling of query parameters in the plugin's functionality. The vulnerability manifests when the plugin processes user input through the add_query_arg function, which is commonly used in WordPress to manipulate URL query strings. The flaw allows attackers to inject malicious scripts into URLs that are subsequently processed and displayed to other users, creating a persistent XSS vector within the WordPress environment.
The technical root cause of this vulnerability stems from insufficient input sanitization and output escaping within the plugin's codebase. When the mailchimp-for-wp plugin utilizes the add_query_arg function to construct URLs for redirection or return paths, it fails to properly sanitize the input parameters before incorporating them into the final URL structure. This creates an opportunity for malicious actors to inject script code through crafted query parameters that are then executed in the browsers of unsuspecting users who visit pages containing these malformed URLs. The vulnerability specifically impacts how the plugin handles return values from add_query_arg, which is a standard WordPress function designed to add or update query arguments in URLs.
The operational impact of this vulnerability extends beyond simple script execution, as it provides attackers with potential access to user sessions and sensitive data within the WordPress environment. When exploited, the XSS vulnerability allows attackers to steal cookies, session tokens, and potentially escalate privileges within the WordPress admin interface. The vulnerability is particularly concerning because it affects a widely used plugin that integrates with Mailchimp services, meaning that compromised sites could be used to harvest user email addresses and other personal information. The attack surface is broad since the vulnerability can be triggered through various user interactions that lead to URL generation within the plugin's functionality.
Mitigation strategies for this vulnerability require immediate plugin updates to version 4.1.8 or later, which contain the necessary patches to address the XSS flaw. System administrators should also implement proper input validation and output escaping mechanisms throughout their WordPress installations, particularly around functions that handle URL parameters and query strings. The vulnerability aligns with CWE-79 Cross-site Scripting and follows patterns commonly associated with ATT&CK technique T1566.001 Phishing, where attackers leverage XSS vulnerabilities to redirect users to malicious sites or steal session information. Organizations should also consider implementing Content Security Policy headers to provide additional protection against script injection attacks, though this serves as a supplementary defense rather than a complete remediation for the underlying vulnerability.
The broader implications of this vulnerability highlight the critical importance of plugin security auditing and regular update management in WordPress environments. Given that many WordPress sites rely on third-party plugins for core functionality, vulnerabilities in these components can have cascading effects throughout the entire web infrastructure. The mailchimp-for-wp plugin's widespread adoption means that this vulnerability likely affected numerous websites, making it a significant concern for security professionals managing multiple WordPress installations. Proper security monitoring and incident response procedures should include checking for vulnerable plugin versions and implementing automated patch management solutions to prevent exploitation of similar vulnerabilities in the future.