CVE-2020-5502 in phpBB
Summary
by MITRE
phpBB 3.2.8 allows a CSRF attack that can approve pending group memberships.
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Analysis
by VulDB Data Team • 01/15/2020
The vulnerability CVE-2020-5502 represents a cross-site request forgery flaw in phpBB version 3.2.8 that specifically targets the group membership approval functionality within the forum software. This issue arises from the absence of proper anti-CSRF token validation in the group approval process, creating a significant security weakness that can be exploited by malicious actors to manipulate user group memberships without proper authorization. The vulnerability affects the core authentication and authorization mechanisms of the phpBB platform, potentially allowing attackers to elevate user privileges or manipulate group access controls.
The technical implementation of this CSRF vulnerability stems from the lack of secure token verification during the group membership approval workflow. When administrators or authorized users attempt to approve pending group memberships, the phpBB application fails to validate that the request originates from a legitimate source within the same session. This absence of CSRF protection means that an attacker can craft malicious web pages or email attachments that, when visited by an authenticated user, automatically submit approval requests for pending group memberships. The flaw exists in the application's web interface layer where the approval actions are processed without sufficient validation of the request source or user intent.
The operational impact of this vulnerability extends beyond simple privilege escalation, potentially enabling attackers to gain unauthorized access to restricted forum areas, manipulate user permissions, or compromise the integrity of group-based access controls. An attacker could leverage this vulnerability to approve malicious users into sensitive groups, such as administrators or moderators, thereby gaining elevated privileges within the forum environment. The consequences are particularly severe in environments where phpBB serves as a community platform with multiple user roles and group-based permissions, as successful exploitation could lead to complete compromise of the forum's user management system. This vulnerability aligns with CWE-352, which specifically addresses cross-site request forgery weaknesses in web applications.
Mitigation strategies for CVE-2020-5502 involve immediate patching of the phpBB application to version 3.2.9 or later, which includes the necessary CSRF token validation fixes. Organizations should also implement additional security measures such as monitoring for unauthorized group membership changes, implementing proper access controls, and conducting regular security assessments of their web applications. The fix typically involves adding proper CSRF token generation and validation mechanisms to the group approval process, ensuring that each request contains a unique token that can only be validated within the legitimate session context. Security teams should also consider implementing web application firewalls to detect and block suspicious requests, while following ATT&CK framework techniques for defending against credential access and privilege escalation attacks that could exploit this vulnerability.