CVE-2020-4050 in WordPress
Summary
by MITRE
In affected versions of WordPress, misuse of the `set-screen-option` filter's return value allows arbitrary user meta fields to be saved. It does require an admin to install a plugin that would misuse the filter. Once installed, it can be leveraged by low privileged users. This has been patched in version 5.4.2, along with all the previously affected versions via a minor release (5.3.4, 5.2.7, 5.1.6, 5.0.10, 4.9.15, 4.8.14, 4.7.18, 4.6.19, 4.5.22, 4.4.23, 4.3.24, 4.2.28, 4.1.31, 4.0.31, 3.9.32, 3.8.34, 3.7.34).
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Analysis
by VulDB Data Team • 10/24/2020
The vulnerability described in CVE-2020-4050 represents a critical privilege escalation issue within the WordPress content management system that stems from improper handling of the set-screen-option filter's return value. This flaw exists in WordPress versions prior to 5.4.2 and allows low-privilege users to manipulate user meta fields through malicious plugin installations, creating a significant security risk that can be exploited without requiring administrative credentials initially. The vulnerability operates through a sophisticated manipulation of WordPress's internal filtering mechanism that controls screen options and user preferences.
The technical implementation of this vulnerability relies on the misuse of WordPress's set-screen-option filter which is designed to allow plugins to modify screen options for users. When a malicious plugin installs itself and exploits this filter, it can manipulate the return value to bypass normal validation checks for user meta fields. This allows unauthorized users to write arbitrary data to user meta fields, effectively enabling them to modify user settings, permissions, or other sensitive metadata that should normally be restricted to administrators. The vulnerability specifically affects how WordPress validates and processes the return values from the set-screen-option filter, creating a pathway for privilege escalation.
From an operational impact perspective, this vulnerability represents a serious threat to WordPress installations as it can be leveraged by attackers with minimal privileges to gain elevated access to user accounts and potentially compromise entire sites. The requirement for an admin to install a malicious plugin creates a unique attack vector that combines social engineering with technical exploitation, making it particularly dangerous in environments where administrators frequently install third-party plugins. Once exploited, attackers can manipulate user meta fields to gain persistent access, modify user capabilities, or create backdoors within the system. The vulnerability affects multiple WordPress versions across different release branches, making it widespread and difficult to fully mitigate without patching all affected versions.
The mitigation strategy for CVE-2020-4050 involves immediate patching of all affected WordPress installations to version 5.4.2 or later, with the additional minor releases providing security updates for previously affected versions. Organizations should conduct comprehensive security audits of all installed plugins to identify any potentially malicious code that might exploit this vulnerability, as the attack requires an initial plugin installation. System administrators should implement strict plugin vetting procedures and maintain updated security monitoring to detect unauthorized plugin installations. The vulnerability aligns with CWE-225, which covers improper handling of security-sensitive data, and represents a technique that could be categorized under ATT&CK tactic TA0004 (Privilege Escalation) and technique T1078 (Valid Accounts) when exploited for persistent access to user accounts. Regular security assessments and automated patch management systems are essential to prevent exploitation of this class of vulnerability.