CVE-2021-42547 in Out-of-the-Box Plugin
Summary
by MITRE • 12/13/2021
Insufficient Input Validation in the search functionality of Wordpress plugin Out-of-the-Box prior to 1.20.3 allows unauthenticated user to craft a reflected Cross-Site Scripting attack.
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Analysis
by VulDB Data Team • 12/16/2021
The vulnerability CVE-2021-42547 represents a critical security flaw in the Out-of-the-Box WordPress plugin, specifically within its search functionality. This issue affects versions prior to 1.20.3 and demonstrates a classic case of insufficient input validation that enables malicious actors to execute reflected cross-site scripting attacks without requiring authentication. The vulnerability stems from the plugin's failure to properly sanitize user input when processing search queries, creating an avenue for attackers to inject malicious scripts into web pages viewed by other users.
The technical implementation of this vulnerability resides in how the plugin handles search parameters submitted through HTTP requests. When users enter search terms into the plugin's search interface, the input is not adequately filtered or escaped before being rendered back to the browser. This reflected XSS vulnerability occurs because the plugin directly incorporates user-supplied data into dynamically generated web content without proper sanitization measures. The flaw aligns with CWE-79 which specifically addresses Cross-Site Scripting vulnerabilities where untrusted data is improperly incorporated into web pages without adequate validation or escaping.
From an operational perspective, this vulnerability presents significant risks to WordPress site administrators and their visitors. An attacker can craft malicious search queries containing JavaScript payloads that execute in the context of other users' browsers when they encounter the reflected content. This could lead to session hijacking, credential theft, redirection to malicious sites, or the execution of arbitrary commands on affected systems. The unauthenticated nature of the attack means that anyone can exploit this vulnerability without requiring valid credentials, making it particularly dangerous for publicly accessible websites that utilize the affected plugin.
The impact extends beyond simple script execution as this vulnerability can be leveraged as a stepping stone for more sophisticated attacks within the compromised environment. Attackers can use the reflected XSS to establish persistent access patterns, harvest cookies and session tokens, or redirect users to phishing sites that mimic legitimate WordPress interfaces. According to ATT&CK framework category T1566, this vulnerability represents a technique for initial access through social engineering, where the malicious payloads are delivered via crafted search parameters that appear legitimate to end users. The vulnerability also aligns with T1059 which covers command and scripting interpreter techniques, as the injected scripts can execute arbitrary code within user browsers.
Mitigation strategies for CVE-2021-42547 primarily focus on immediate remediation through plugin updates to version 1.20.3 or later, which contains the necessary input validation fixes. System administrators should also implement additional protective measures such as web application firewalls that can detect and block suspicious search parameter patterns, input sanitization at the application level, and regular security auditing of installed plugins. Organizations should conduct comprehensive vulnerability assessments to identify other potentially affected plugins and ensure that all WordPress installations maintain current versions of core software and extensions. The vulnerability serves as a reminder of the critical importance of input validation and output escaping in web applications, particularly in content management systems where user-generated input is frequently processed and displayed.