CVE-2020-36172 in Advanced Custom Fields Plugin
Summary
by MITRE • 01/07/2021
The Advanced Custom Fields plugin before 5.8.12 for WordPress mishandles the escaping of strings in Select2 dropdowns, potentially leading to XSS.
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Analysis
by VulDB Data Team • 07/08/2026
The vulnerability in the Advanced Custom Fields plugin affects versions prior to 5812 and relates to improper handling of string escaping within Select2 dropdown implementations. This flaw creates a potential cross-site scripting attack vector that could be exploited by malicious actors to inject and execute arbitrary javascript code within the context of a victim's browser session. The issue specifically manifests when the plugin processes user input for select dropdown elements, failing to adequately sanitize or escape special characters that could be interpreted as executable code.
The technical implementation flaw stems from insufficient input validation and output escaping mechanisms within the plugin's frontend rendering logic. When users interact with Select2 dropdowns populated by custom field data, the plugin does not properly encode potentially dangerous characters such as angle brackets, quotes, or javascript protocol handlers that could be leveraged to construct malicious payloads. This vulnerability directly maps to CWE-79 - Improper Neutralization of Input During Web Page Generation into a Different Plane and aligns with ATT&CK technique T1059.007 for script injection attacks.
The operational impact of this vulnerability extends beyond simple data corruption, as successful exploitation could allow attackers to hijack user sessions, steal sensitive information, or manipulate the plugin's functionality. An attacker could craft malicious input containing javascript payloads that would be executed when other users view pages containing affected custom fields. This creates a persistent threat vector within wordpress installations where the plugin is actively used for content management and form creation. The vulnerability affects both administrators and regular users who interact with pages containing compromised select dropdown elements, making it particularly dangerous in multi-user environments.
Mitigation strategies should include immediate upgrade to Advanced Custom Fields version 5812 or later, which contains proper input sanitization and output escaping mechanisms. Organizations should also implement additional security measures such as content security policies that restrict script execution from untrusted sources and regular monitoring of plugin updates. The vulnerability demonstrates the importance of proper input validation at multiple layers within web applications, particularly when dealing with dynamic content rendering and user-provided data in javascript-based components. Security teams should conduct thorough assessments of all installed plugins for similar escaping issues and establish automated update procedures to maintain protection against known vulnerabilities.
The flaw highlights common security pitfalls in wordpress plugin development where developers may overlook the need for comprehensive output encoding in javascript contexts, particularly when integrating third-party libraries like Select2 that handle dynamic data rendering. This vulnerability serves as a reminder of the critical importance of maintaining proper security hygiene throughout the software development lifecycle and demonstrates how seemingly minor implementation oversights can create significant attack surface exposure within content management systems.