CVE-2021-39325 in OptinMonster Plugin
Summary
by MITRE • 09/21/2021
The OptinMonster WordPress plugin is vulnerable to Reflected Cross-Site Scripting due to insufficient input validation in the load_previews function found in the ~/OMAPI/Output.php file which allows attackers to inject arbitrary web scripts, in versions up to and including 2.6.0.
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Analysis
by VulDB Data Team • 09/29/2021
The vulnerability identified as CVE-2021-39325 affects the OptinMonster WordPress plugin, a popular tool for creating and managing opt-in forms and lead generation campaigns. This issue resides within the OMAPI/Output.php file where the load_previews function fails to properly validate and sanitize user input parameters. The flaw represents a classic reflected cross-site scripting vulnerability that occurs when the plugin fails to adequately filter or escape data received from HTTP request parameters before rendering it in web responses. Attackers can exploit this weakness by crafting malicious URLs containing script payloads that get executed in the context of authenticated users' browsers when they access the vulnerable plugin functionality.
The technical implementation of this vulnerability stems from the plugin's insufficient input validation mechanisms within the load_previews function. When users interact with the plugin's preview features, the system accepts parameters directly from the HTTP request without proper sanitization. This creates an opportunity for malicious actors to inject HTML or JavaScript code through URL parameters that are then reflected back to the user's browser. The vulnerability specifically impacts versions up to and including 2.6.0, indicating that the developers may have addressed similar issues in later releases but failed to completely resolve the input validation gap. This flaw aligns with CWE-79 which categorizes cross-site scripting vulnerabilities as a result of inadequate input validation and output encoding.
The operational impact of this vulnerability is significant for WordPress site administrators who use the OptinMonster plugin. An attacker could potentially execute malicious scripts in the browsers of authenticated users, potentially leading to session hijacking, credential theft, or unauthorized actions within the WordPress admin interface. Since the vulnerability affects the plugin's preview functionality, attackers might craft malicious links that, when clicked by administrators or other privileged users, could execute arbitrary code. This could enable attackers to gain elevated privileges, modify content, or even take complete control of the WordPress installation. The reflected nature of the vulnerability means that the attack payload is delivered through a URL that, when accessed, immediately executes the malicious code in the victim's browser context. This makes the vulnerability particularly dangerous as it requires minimal user interaction beyond simply visiting the malicious link.
Mitigation strategies for this vulnerability should prioritize immediate remediation through plugin updates to versions that address the input validation issues. System administrators should ensure that all WordPress installations running the affected plugin are updated to the latest available version where the vulnerability has been patched. Additionally, implementing proper input validation and output encoding measures can help prevent similar issues in the future. Organizations should consider implementing web application firewalls that can detect and block suspicious script payloads in HTTP requests. Regular security audits of WordPress plugins and themes should be conducted to identify and remediate similar vulnerabilities. The ATT&CK framework categorizes this type of vulnerability under T1213 - Data from Information Repositories, as attackers could potentially extract sensitive data through XSS attacks, and T1059 - Command and Scripting Interpreter, when attackers use the vulnerability to execute malicious commands in the victim's browser environment.