CVE-2021-24871 in Get Custom Field Values Plugin
Summary
by MITRE • 12/13/2021
The Get Custom Field Values WordPress plugin before 4.0.1 does not escape custom fields before outputting them in the page, which could allow users with a role as low as contributor to perform Cross-Site Scripting attacks
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Analysis
by VulDB Data Team • 12/16/2021
The CVE-2021-24871 vulnerability affects the Get Custom Field Values WordPress plugin version 4.0.1 and earlier, presenting a critical cross-site scripting risk that can be exploited by low-privilege users. This vulnerability stems from improper output escaping of custom field values within the plugin's functionality, creating a pathway for malicious actors to inject arbitrary scripts into web pages viewed by other users. The flaw specifically targets the plugin's handling of user-generated content within custom fields, where data is rendered without adequate sanitization measures.
The technical implementation of this vulnerability lies in the plugin's failure to apply proper escaping mechanisms when displaying custom field values on web pages. When contributors or other users with minimal privileges create or modify custom fields containing malicious script content, the plugin processes this data without appropriate HTML escaping or output encoding. This oversight allows attackers to inject JavaScript code that executes in the context of other users' browsers when they view pages containing these compromised custom fields. The vulnerability is particularly concerning because it requires minimal privilege levels to exploit, making it accessible to users who should typically have restricted capabilities within WordPress environments.
From an operational impact perspective, this vulnerability can enable attackers to perform various malicious activities including session hijacking, credential theft, data exfiltration, and redirection to malicious sites. The low privilege requirement means that even users with contributor roles can potentially compromise the security of an entire WordPress site. Attackers could craft custom field content that, when viewed by administrators or other high-privilege users, executes scripts to steal cookies, modify content, or establish persistent access points. The vulnerability affects all WordPress installations using the vulnerable plugin version, regardless of theme or other plugins present, making it a widespread concern for site administrators.
Security professionals should implement immediate mitigations including updating the Get Custom Field Values plugin to version 4.0.1 or later, where the escaping issues have been resolved. Additionally, administrators should review existing custom field content for potential malicious scripts and consider implementing additional security measures such as content security policies and regular security audits. The vulnerability aligns with CWE-79 which describes cross-site scripting flaws, and maps to ATT&CK technique T1566 for social engineering attacks that leverage web-based vulnerabilities. Organizations should also consider implementing web application firewalls and monitoring for unusual custom field modifications that could indicate exploitation attempts. Regular vulnerability scanning and patch management processes become critical to prevent exploitation of similar output encoding flaws in other WordPress plugins and web applications.