CVE-2017-17451 in WP Mailster Plugin
Summary
by MITRE
The WP Mailster plugin before 1.5.5 for WordPress has XSS in the unsubscribe handler via the mes parameter to view/subscription/unsubscribe2.php.
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Analysis
by VulDB Data Team • 01/17/2023
The WP Mailster plugin vulnerability CVE-2017-17451 represents a critical cross-site scripting flaw that affects versions prior to 1.5.5 within the WordPress ecosystem. This vulnerability specifically targets the unsubscribe functionality of the plugin, creating a pathway for malicious actors to inject arbitrary web scripts into the application's response. The flaw manifests when the mes parameter is passed to the view/subscription/unsubscribe2.php endpoint, allowing attackers to manipulate the unsubscribe handler and execute malicious code within the context of a victim's browser session. The vulnerability resides in the plugin's insufficient input validation and output sanitization mechanisms, which fail to properly escape or filter user-supplied data before incorporating it into the response. This particular attack vector demonstrates how email marketing plugins can become entry points for broader security compromises, as the unsubscribe feature is frequently accessed by end users who may unknowingly trigger malicious payloads. The vulnerability is categorized under CWE-79 as a cross-site scripting weakness, specifically targeting the failure to sanitize user input before rendering it in web pages. From an operational perspective, this vulnerability enables attackers to perform session hijacking, deface websites, steal sensitive cookies, or redirect users to malicious domains. The attack requires minimal privileges since it operates through the standard unsubscribe workflow that users interact with regularly, making it particularly dangerous in environments where users may not be security-aware. The issue aligns with ATT&CK technique T1566.001 which covers spearphishing attachments, as users might be tricked into clicking malicious unsubscribe links that exploit this vulnerability. The impact extends beyond simple script execution, potentially allowing attackers to establish persistent access or conduct further reconnaissance within the compromised WordPress environment.
The technical implementation of this vulnerability stems from the plugin's failure to properly sanitize the mes parameter before using it in the unsubscribe handler. When a user clicks an unsubscribe link, the mes parameter contains encoded data that should be processed safely, but the plugin's code directly incorporates this parameter into HTML output without appropriate encoding or validation. This oversight creates a classic XSS scenario where attacker-controlled data flows from the input parameter through the application logic to the browser output. The vulnerability is particularly concerning because unsubscribe functionality is a standard feature that users trust and frequently interact with, making social engineering attacks more effective. The flaw exists in the plugin's view/subscription/unsubscribe2.php file where the mes parameter is processed without adequate sanitization, allowing HTML characters to be interpreted as executable script code. This type of vulnerability represents a common pattern in web applications where developers assume that certain parameters are safe or fail to implement proper output encoding for dynamic content. The security implications are significant as this vulnerability can be exploited through various attack vectors including email phishing campaigns, where attackers craft malicious unsubscribe links that target the vulnerable plugin version. The vulnerability's exploitation does not require authentication or administrative privileges, making it accessible to any user with access to the affected WordPress site.
Mitigation strategies for CVE-2017-17451 should prioritize immediate plugin updates to version 1.5.5 or later, which contains the necessary fixes for the XSS vulnerability. Organizations should also implement comprehensive input validation and output encoding practices throughout their WordPress installations to prevent similar issues in other plugins or custom code. Security headers including Content Security Policy should be configured to limit script execution and prevent unauthorized code injection. Regular security audits of WordPress plugins and themes are essential to identify and remediate vulnerabilities before they can be exploited. Network monitoring solutions should be configured to detect suspicious patterns in unsubscribe link usage that might indicate exploitation attempts. The vulnerability demonstrates the importance of proper parameter validation and output encoding as outlined in OWASP Top 10 2021 category A03: Injection, which includes XSS as a primary concern. System administrators should also consider implementing web application firewalls to detect and block malicious requests targeting known vulnerable endpoints. User education programs should emphasize the risks of clicking unsubscribe links from unknown sources and the importance of verifying email authenticity before interacting with marketing communications. The vulnerability highlights the need for security awareness training that addresses how email marketing systems can become attack vectors, particularly in enterprise environments where large volumes of email traffic are processed through WordPress platforms. Additionally, organizations should maintain updated vulnerability databases and automated scanning tools to identify unpatched versions of plugins across their WordPress installations. The remediation process should include thorough testing of the updated plugin to ensure that the fix does not introduce compatibility issues with existing email campaigns or subscription workflows.