CVE-2018-20423 in DiscuzX
Summary
by MITRE
Discuz! DiscuzX 3.4, when WeChat login is enabled, allows remote attackers to bypass a "disabled registration" setting by adding a non-existing wxopenid value to the plugin.php ac=wxregister query string.
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Analysis
by VulDB Data Team • 04/23/2020
The vulnerability identified as CVE-2018-20423 affects Discuz! DiscuzX 3.4 platforms that have WeChat login functionality enabled. This security flaw represents a critical authorization bypass issue that undermines the platform's user registration controls. The vulnerability specifically targets the authentication mechanism when users attempt to register through WeChat integration, creating an exploitable path that allows unauthorized user creation despite explicit system configurations that should disable new registrations.
The technical implementation of this vulnerability exploits a weakness in the plugin.php script's handling of the wxregister action parameter. When attackers manipulate the query string by adding a non-existing wxopenid value, the system fails to properly validate whether registration is permitted according to the platform's configuration settings. This flaw occurs because the authentication flow does not adequately verify the system's registration disabled status before processing WeChat login attempts. The vulnerability essentially allows attackers to circumvent access control mechanisms that should prevent new user accounts from being created, regardless of the platform's administrative configuration.
From an operational impact perspective, this vulnerability creates significant security risks for Discuz! communities that rely on WeChat integration for user authentication. Attackers can exploit this flaw to create unauthorized user accounts, potentially leading to spam registration, forum abuse, and the establishment of malicious user profiles. The bypass of the registration disable setting means that even organizations that have explicitly configured their platforms to prevent new user creation can have their security policies circumvented. This vulnerability particularly affects community platforms where user-generated content is prevalent and where controlling user access is critical for maintaining platform integrity and preventing abuse.
The vulnerability aligns with CWE-602, which addresses client-side enforcement of server-side security checks, and represents a classic example of insufficient validation of access control mechanisms. From an ATT&CK framework perspective, this vulnerability maps to T1078 Valid Accounts and T1566 Phishing, as it enables attackers to create legitimate-looking user accounts that can be used for further malicious activities. The exploitation process requires minimal technical skill and can be automated, making it particularly dangerous for widespread abuse. Organizations should implement immediate mitigations including disabling WeChat login functionality until a proper patch is applied, or implementing additional validation layers to verify registration settings before processing WeChat authentication requests. The vulnerability demonstrates the critical importance of maintaining proper input validation and access control enforcement in web applications, particularly when integrating third-party authentication services.