CVE-2021-20867 in Advanced Custom Fields Plugin
Summary
by MITRE • 12/13/2021
Advanced Custom Fields versions prior to 5.11 and Advanced Custom Fields Pro versions prior to 5.11 contain a missing authorization vulnerability in moving the field group which may allow a user to move the unauthorized field group via unspecified vectors.
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Analysis
by VulDB Data Team • 12/15/2021
The vulnerability identified as CVE-2021-20867 affects the Advanced Custom Fields plugin ecosystem, specifically versions prior to 5.11 for both the standard and Pro editions. This represents a critical authorization flaw that undermines the security controls designed to protect field group configurations within WordPress environments. The issue manifests as a missing authorization check during field group movement operations, creating a pathway for unauthorized users to manipulate content structure and potentially access sensitive data.
The technical implementation of this vulnerability stems from inadequate access control validation within the plugin's administrative interface. When users attempt to move field groups between locations, the system fails to properly verify whether the authenticated user possesses the necessary permissions to perform such operations. This authorization gap exists across unspecified vectors, suggesting the flaw may be present in multiple interaction points within the plugin's user management and field group manipulation components. The vulnerability aligns with CWE-863, which specifically addresses "Incorrect Authorization" conditions where the system fails to properly validate user permissions before executing privileged operations. From an attack perspective, this weakness enables privilege escalation through unauthorized field group manipulation, potentially allowing attackers to reorganize content structures in ways that could expose sensitive information or disrupt content management workflows.
The operational impact of this vulnerability extends beyond simple unauthorized access, as it can compromise the integrity and confidentiality of WordPress content management systems. Attackers with minimal privileges could leverage this flaw to move field groups containing sensitive data, potentially exposing administrative configurations or user information to unauthorized parties. The implications are particularly severe in multi-user environments where different roles have distinct permission levels, as this vulnerability could enable lower-privileged users to gain access to higher-level content structures. This weakness directly impacts the principle of least privilege and can be categorized under ATT&CK technique T1078.004, which addresses valid accounts used for unauthorized access, as it allows unauthorized movement of administrative components without proper authorization checks.
Mitigation strategies should prioritize immediate patching of affected systems to version 5.11 or later, which includes the necessary authorization controls to prevent unauthorized field group movements. Administrators should also implement additional security measures including regular security audits of plugin configurations, monitoring of administrative activities, and enforcement of strict role-based access controls within WordPress environments. The remediation process should include verification that all field groups are properly secured through appropriate user permissions and that no unauthorized movement operations have occurred since the vulnerability was introduced. Organizations should also consider implementing network-level controls and intrusion detection systems to monitor for suspicious administrative activities that might indicate exploitation attempts. Regular security assessments of WordPress plugins and themes remain essential to identify similar authorization gaps that could compromise system integrity and user data protection.