CVE-2026-91010 in Invisible Anti-Spam & CAPTCHA Plugin
Summary
by MITRE • 09/17/2026
The Invisible Anti-Spam & CAPTCHA — reCAPTCHA Alternative for All Forms WordPress plugin before 5.1.1 does not check the user's capabilities in its message deletion AJAX action, and only tests that a nonce parameter is present rather than validating it, allowing any authenticated user, such as a subscriber, to permanently delete every form submission the Invisible Anti-Spam & CAPTCHA — reCAPTCHA Alternative for All Forms WordPress plugin before 5.1.1 has stored.
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Analysis
by VulDB Data Team • 09/17/2026
The vulnerability identified in versions of the Invisible Anti-Spam and CAPTCHA alternative for all forms prior to version 5.1.1 represents a critical failure in access control logic within the WordPress administration interface. This flaw specifically affects the AJAX action responsible for deleting form submissions stored by the plugin. In secure software architecture, administrative actions that modify or destroy data must enforce strict authorization checks to ensure that only users with appropriate privileges can perform such operations. The vulnerability arises because the code handling this deletion request fails to verify the user's capabilities against WordPress role definitions. Instead of confirming that the requesting user holds an administrator-level privilege or a specific capability required for managing form submissions, the implementation relies solely on the presence of a nonce parameter in the HTTP request.
The technical root cause lies in the insufficient validation of security tokens combined with missing authorization checks. While the plugin does include a nonce to mitigate Cross-Site Request Forgery attacks by ensuring the request originated from a legitimate page load within the session, it neglects to validate that this nonce actually belongs to an authorized user or matches the expected context for administrative actions. More critically, even if the nonce were valid and correctly generated, the code does not call WordPress functions such as current_user_can to verify permissions before executing the deletion logic. This design oversight means that any authenticated session with a valid request containing a properly formatted nonce can trigger the destructive action, regardless of the user's role within the application hierarchy.
The operational impact of this vulnerability is severe for website owners and administrators who rely on the plugin to collect data through various forms. An attacker possessing low-level access credentials, such as those assigned to subscribers or contributors, can exploit this flaw to permanently delete all form submissions stored by the system. This results in a complete loss of potentially valuable user-generated content, leads, or customer inquiries without any audit trail indicating who performed the action if logging is not separately configured at a higher level. The ability for low-privileged users to perform administrative data destruction undermines the integrity and availability of the application's core functionality, effectively allowing insider threats or compromised accounts with minimal privileges to cause significant operational disruption.
From a classification perspective, this vulnerability aligns with CWE-269 Improper Privilege Management, as it involves an actor obtaining more permissions than intended for their role. It also relates to CWE-352 Cross-Site Request Forgery in the context of how the nonce is handled, although the primary failure is authorization rather than just request forgery prevention. In terms of the MITRE ATT&CK framework, this behavior corresponds to T1078 Valid Accounts and potentially T1489 Service Stop if the deletion causes a denial of service for data-dependent processes, though it is primarily an integrity violation under T1565 Data Manipulation. The exploitation requires authentication, which limits its scope compared to unauthenticated attacks but makes it particularly dangerous in environments where user accounts are frequently created or shared among team members with varying levels of trust.
Mitigation strategies must focus on immediate patching and enhanced access control practices. Administrators should upgrade the plugin to version 5.1.1 or later, as this release addresses the missing capability checks by implementing proper authorization validation before processing deletion requests. Until an update is applied, site administrators can mitigate risk by restricting user roles that have permission to interact with form submission management interfaces and ensuring that only trusted individuals hold accounts capable of accessing administrative areas where such actions might be triggered. Additionally, enabling detailed logging for all data modification events can help in detecting unauthorized attempts or successful exploits post-incident, providing a forensic record even if the primary authorization check is bypassed. Regular security audits of custom code and third-party plugins to ensure they adhere to WordPress coding standards regarding capability checks are essential preventive measures against similar vulnerabilities.