CVE-2026-16604 in Passster Plugin
Summary
by MITRE • 08/05/2026
The Passster WordPress plugin before 4.3.6 outputs password-protected block content in the public page response before verifying the password, allowing unauthenticated users to recover the protected content without knowing the password.
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Analysis
by VulDB Data Team • 08/05/2026
The Passster WordPress plugin vulnerability represents a critical access control flaw that undermines the fundamental security mechanism designed to protect sensitive content. This issue affects versions prior to 4.3.6 and stems from improper authentication verification within the plugin's block rendering logic. The vulnerability manifests when password-protected content blocks are processed and returned in public page responses without first validating whether the requesting user has provided the correct password. This design flaw creates an inherent bypass mechanism that allows any unauthenticated visitor to access content that should remain protected behind a password barrier.
The technical nature of this vulnerability aligns with CWE-284 Access Control Bypass, where insufficient authorization checks permit unauthorized access to protected resources. The flaw operates at the application logic level rather than affecting underlying system components or network protocols. When WordPress processes a page containing password-protected blocks, the plugin fails to perform proper authentication verification before rendering the content. This creates a scenario where the system returns sensitive data in clear text format within public HTTP responses, effectively neutralizing the password protection mechanism that users rely upon to secure their content.
From an operational standpoint, this vulnerability has severe implications for website administrators and content owners who depend on password-protected content for confidentiality. Attackers can exploit this weakness to harvest protected information including private documents, restricted access areas, or sensitive business data without requiring any credentials or authentication attempts. The impact extends beyond simple content exposure as it may lead to unauthorized access to proprietary information, intellectual property theft, or violation of privacy regulations. Organizations using WordPress with Passster plugin versions prior to 4.3.6 face potential compliance violations under data protection frameworks such as gdpr, ccpa, and other regulatory requirements that mandate proper access controls for sensitive content.
The attack vector for this vulnerability is straightforward and requires no specialized tools or techniques beyond basic web browsing capabilities. An attacker simply needs to navigate to a public page containing password-protected blocks and observe the unfiltered content in the page response. This makes the vulnerability particularly dangerous as it can be exploited at scale without requiring significant technical expertise. The lack of authentication verification during content rendering creates a persistent risk that remains active until the plugin is updated to version 4.3.6 or later, making it an attractive target for automated scanning tools and malicious actors seeking to exploit weak access controls.
Mitigation strategies should prioritize immediate plugin updates to version 4.3.6 or higher where the vulnerability has been addressed through proper authentication verification mechanisms. System administrators should conduct comprehensive audits of all WordPress installations using Passster plugin to identify affected versions and implement patch management processes. Additional defensive measures include monitoring web server logs for unusual access patterns, implementing rate limiting on content requests, and considering temporary workarounds such as disabling password-protected blocks until updates are deployed. Organizations should also review their overall WordPress security posture, including regular vulnerability scanning, secure configuration practices, and proper access control implementations to prevent similar issues from occurring in other components of their web infrastructure. The remediation process must include thorough testing of updated plugin functionality to ensure that legitimate password protection continues to work as intended while addressing the specific bypass vulnerability that allowed unauthorized content access.