CVE-2021-4407 in Custom Banners Plugin
Summary
by MITRE • 07/12/2023
The Custom Banners plugin for WordPress is vulnerable to Cross-Site Request Forgery in versions up to, and including, 3.2.2 This is due to missing or incorrect nonce validation on the saveCustomFields() function. This makes it possible for unauthenticated attackers to save custom fields via a forged request granted they can trick a site administrator into performing an action such as clicking on a link.
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Analysis
by VulDB Data Team • 07/12/2023
The Custom Banners plugin for WordPress represents a widely used tool for managing and displaying banner content across websites, with version 3.2.2 containing a critical cross-site request forgery vulnerability that affects installations up to and including this release. This vulnerability resides within the saveCustomFields() function which fails to implement proper nonce validation mechanisms, creating a significant security gap that can be exploited by malicious actors without authentication requirements. The flaw specifically targets the plugin's administrative functionality, where unauthorized parties can manipulate banner configurations through crafted requests that appear legitimate to the WordPress system.
The technical nature of this vulnerability stems from the absence of proper cryptographic token verification within the plugin's processing logic. Nonce validation serves as a critical security control that ensures requests originate from legitimate administrative sessions by generating time-sensitive tokens that are validated against expected values. Without this validation, attackers can construct malicious requests that bypass the normal authentication and authorization checks typically required for administrative operations. The vulnerability enables attackers to manipulate custom field data within the plugin's configuration system, potentially allowing them to modify banner content, alter display settings, or even inject malicious configurations that could affect site functionality and security posture.
The operational impact of this vulnerability extends beyond simple data manipulation, as it creates a persistent threat vector that can be exploited to compromise WordPress administrative privileges and potentially escalate attacks. An attacker need only trick a site administrator into clicking a malicious link or visiting a compromised page to execute unauthorized actions, making this vulnerability particularly dangerous in environments where administrators frequently browse external sites or receive phishing emails. The lack of authentication requirements means that even basic website visitors could potentially exploit this flaw if they can successfully craft and deliver a forged request to an administrator. This vulnerability directly aligns with attack patterns described in the attack technique matrix under credential exposure and privilege escalation categories, where attackers leverage insufficient validation controls to perform unauthorized operations.
Mitigation strategies for this vulnerability should prioritize immediate plugin updates to versions that include proper nonce validation mechanisms, while administrators should implement additional security measures such as restricting administrative access through network-level controls and monitoring for suspicious activity within the plugin's administrative interfaces. Organizations should also consider implementing web application firewalls that can detect and block suspicious request patterns targeting known vulnerable endpoints, and conduct regular security audits of installed WordPress plugins to identify similar validation gaps. The vulnerability demonstrates the critical importance of proper input validation and authentication controls within web applications, aligning with common weakness enumerations in the CWE database that specifically address insufficient validation of cryptographic tokens and improper access control mechanisms. Security teams should also establish incident response procedures to quickly address potential exploitation attempts and monitor for signs of compromise within their WordPress installations.