CVE-2016-9403 in MyBB
Summary
by MITRE
newreply.php in MyBB (aka MyBulletinBoard) before 1.8.7 and MyBB Merge System before 1.8.7 allows remote attackers to have unspecified impact by leveraging a missing permission check.
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Analysis
by VulDB Data Team • 08/08/2020
The vulnerability identified as CVE-2016-9403 affects MyBB, a popular bulletin board system, and its associated MyBB Merge System, specifically versions prior to 1.8.7. This security flaw resides within the newreply.php script, which handles the functionality for creating new replies within forum discussions. The vulnerability stems from a critical missing permission check that allows unauthenticated or unauthorized users to exploit the system's reply functionality. This represents a significant security oversight as it undermines the fundamental access control mechanisms that should prevent users from performing actions they are not authorized to execute. The missing permission validation creates an entry point for attackers to potentially manipulate forum content or escalate their privileges within the system.
The technical nature of this vulnerability aligns with CWE-284, which describes improper access control issues where systems fail to properly enforce access restrictions. This weakness specifically manifests in the newreply.php script where the application does not adequately verify whether a user possesses the necessary permissions to create replies in specific forums. Attackers can exploit this by crafting malicious requests that bypass the normal authentication and authorization checks, potentially allowing them to post content, modify existing replies, or even gain elevated privileges within the forum environment. The unspecified impact mentioned in the CVE description indicates that the consequences could range from content manipulation to more severe privilege escalation depending on how the vulnerability is leveraged and the specific configuration of the affected system.
From an operational perspective, this vulnerability presents a substantial risk to forum administrators and their users. The impact extends beyond simple content tampering as unauthorized users could potentially flood forums with spam, post malicious links, or manipulate discussion threads to spread misinformation. The vulnerability also creates potential for more serious security implications including the possibility of privilege escalation attacks that could allow attackers to gain administrative access to the forum. Organizations relying on MyBB for community discussions, support systems, or collaborative platforms face significant exposure when running vulnerable versions, as the attack surface expands to include any user who can access the forum interface. The nature of bulletin board systems makes them particularly attractive targets for attackers seeking to establish persistent presence within online communities or to disrupt service availability.
Mitigation strategies for CVE-2016-9403 should prioritize immediate patching of affected systems to version 1.8.7 or later, which contains the necessary permission checks to prevent unauthorized access. System administrators should also implement additional monitoring of forum activities to detect anomalous posting behavior that might indicate exploitation attempts. Network-level controls such as web application firewalls can provide additional protection by blocking suspicious requests to the newreply.php endpoint. Security teams should conduct thorough audits of their MyBB installations to ensure no other components are vulnerable to similar permission bypass issues. The vulnerability demonstrates the critical importance of maintaining up-to-date software and implementing proper access control mechanisms as outlined in the ATT&CK framework's privilege escalation tactics. Organizations should also consider implementing regular security assessments and penetration testing to identify and remediate similar weaknesses in their web applications. The incident highlights the necessity of following secure coding practices and conducting proper code reviews to prevent missing permission checks that could lead to unauthorized system access.