CVE-2017-16562 in UserPro Plugin
Summary
by MITRE
The UserPro plugin before 4.9.17.1 for WordPress, when used on a site with the "admin" username, allows remote attackers to bypass authentication and obtain administrative access via a "true" value for the up_auto_log parameter in the QUERY_STRING to the default URI.
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Analysis
by VulDB Data Team • 11/24/2025
The vulnerability described in CVE-2017-16562 represents a critical authentication bypass flaw within the UserPro plugin for WordPress systems. This weakness specifically affects versions prior to 4.9.17.1 and creates a significant security risk when the WordPress site utilizes the default administrative username "admin". The vulnerability exploits a parameter injection technique that allows remote attackers to manipulate the query string parameters during authentication requests, effectively circumventing the normal login process and gaining unauthorized administrative privileges.
The technical implementation of this vulnerability stems from improper input validation within the UserPro plugin's authentication handling mechanism. When the up_auto_log parameter is manipulated to contain a "true" value in the query string of the default URI, the plugin fails to properly validate this input before processing authentication requests. This lack of proper parameter sanitization creates an injection vector that attackers can exploit to bypass standard authentication controls. The flaw operates at the application layer and demonstrates poor input validation practices that align with CWE-20, which addresses improper input validation in software systems. The vulnerability essentially allows attackers to craft malicious requests that automatically log them in as administrators without requiring valid credentials.
The operational impact of this vulnerability extends beyond simple unauthorized access, as it provides attackers with complete administrative control over affected WordPress installations. Once an attacker successfully exploits this vulnerability, they can modify website content, install malicious plugins, create new administrator accounts, and potentially use the compromised site as a launchpad for further attacks within the network. This authentication bypass represents a severe threat to website integrity and data security, as it allows attackers to operate undetected with full administrative privileges. The risk is particularly elevated when sites use the default "admin" username, as this makes exploitation more straightforward and increases the likelihood of successful attacks. The vulnerability also aligns with ATT&CK technique T1078 which covers legitimate credentials use for persistence and privilege escalation.
Organizations affected by this vulnerability should immediately update to UserPro plugin version 4.9.17.1 or later, which includes proper input validation and authentication controls. System administrators should also implement network monitoring to detect suspicious query string parameters and consider implementing web application firewalls to block malicious requests containing the up_auto_log parameter. Additionally, security teams should conduct thorough audits of all installed WordPress plugins to identify similar vulnerabilities and ensure that default administrative usernames are changed to prevent exploitation of this specific weakness. The remediation process should include comprehensive testing to verify that the update has properly resolved the authentication bypass issue without introducing compatibility problems with existing site functionality.