CVE-2021-4403 in Remove Schema Plugin
Summary
by MITRE • 07/01/2023
The Remove Schema plugin for WordPress is vulnerable to Cross-Site Request Forgery in versions up to, and including, 1.5. This is due to missing or incorrect nonce validation on the validate() function. This makes it possible for unauthenticated attackers to modify the plugins settings 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 • 04/10/2026
The Remove Schema plugin for WordPress presents a critical cross-site request forgery vulnerability that affects versions up to and including 1.5. This vulnerability stems from inadequate security controls within the plugin's validate() function, which fails to properly implement nonce validation mechanisms. The absence of proper nonce verification creates a significant security gap that allows unauthenticated attackers to manipulate plugin settings through maliciously crafted requests. The vulnerability operates under the principle that attackers can deceive administrators into executing unintended actions, making it particularly dangerous in environments where administrators frequently visit external websites or are susceptible to social engineering attacks. The flaw represents a classic csrf attack vector where the attacker crafts a malicious request that appears legitimate to the WordPress system, exploiting the trust relationship between the administrator and the vulnerable plugin.
This vulnerability directly maps to CWE-352, which specifically addresses Cross-Site Request Forgery flaws in web applications. The technical implementation issue lies in the plugin's failure to validate the authenticity of requests through proper nonce mechanisms that WordPress employs to prevent csrf attacks. The validate() function should have implemented wp_verify_nonce() or equivalent validation checks to ensure that requests originate from legitimate administrative sessions. Without these protections, any user who can access the plugin's administrative interface can be exploited by an attacker who crafts a forged request containing malicious parameters. The vulnerability demonstrates a fundamental lack of input validation and authentication checks that should be standard in all WordPress plugin development practices. The attack requires minimal prerequisites since the attacker only needs to convince an administrator to click on a malicious link, making it particularly effective in real-world scenarios.
The operational impact of this vulnerability extends beyond simple configuration changes, as it allows attackers to potentially modify core plugin functionality that could affect website performance, security posture, or even provide additional attack vectors. An attacker could leverage this vulnerability to disable security features, modify schema settings that impact SEO, or potentially gain unauthorized access to sensitive administrative functions. The vulnerability affects all WordPress installations using the affected plugin version, regardless of the underlying WordPress core version, making it a widespread concern. The risk is particularly elevated in environments where multiple administrators have access to the system, as the attack could be executed through any compromised administrator session. The vulnerability also aligns with ATT&CK technique T1078.004 which covers valid accounts used for unauthorized access, as successful exploitation could lead to broader administrative compromise.
Mitigation strategies should focus on immediate plugin updates to versions that address the nonce validation issue, as well as implementing additional security measures such as restricting administrative access through firewall rules, implementing multi-factor authentication, and monitoring for suspicious administrative activities. Administrators should also consider implementing web application firewalls that can detect and block csrf attack patterns, and regularly audit plugin configurations to ensure that only necessary administrative functions are exposed. The vulnerability underscores the importance of proper security testing during plugin development and the necessity of following WordPress security guidelines. Organizations should conduct regular security assessments to identify similar issues in other plugins and ensure that all administrative interfaces implement proper csrf protection mechanisms. Additionally, security awareness training for administrators can help reduce the risk of successful social engineering attacks that exploit this vulnerability.