CVE-2021-3337 in Hide-Thread-Content Plugin
Summary
by MITRE • 01/29/2021
The Hide-Thread-Content plugin through 2021-01-27 for MyBB allows remote attackers to bypass intended content-reading restrictions by clicking on reply or quote in the postbit.
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Analysis
by VulDB Data Team • 12/22/2024
The Hide-Thread-Content plugin for MyBB represents a critical access control vulnerability that undermines the core security model of forum platforms. This vulnerability specifically affects versions through 2021-01-27 and demonstrates a fundamental flaw in how the plugin handles user permissions and content visibility controls. The issue manifests when authenticated users attempt to access restricted content through legitimate forum interactions such as replying to posts or quoting content, which should normally be restricted to authorized users only. The vulnerability exploits a design oversight in the plugin's permission checking mechanisms, allowing unauthorized access to content that should remain hidden from unprivileged users.
The technical implementation of this flaw involves the plugin's failure to properly validate user permissions during postbit interactions. When users click on reply or quote links within forum posts, the system should verify that the requesting user has appropriate access rights to view the hidden content. However, the vulnerability allows attackers to bypass these checks by leveraging the natural forum workflow. This occurs because the plugin does not properly enforce content access restrictions when processing these specific user actions, creating an access bypass that can be exploited through standard forum navigation without requiring elevated privileges or specialized attack tools. The flaw essentially creates a backdoor pathway through which users can circumvent the intended access controls that protect sensitive forum content.
From an operational perspective, this vulnerability poses significant risks to forum administrators and their communities. The bypass allows attackers to access restricted content such as private discussions, member-only threads, or sensitive information that should only be visible to authorized users. This could lead to information disclosure, violation of user privacy expectations, and potential compromise of confidential discussions. The impact extends beyond simple content access, as it undermines the trust users place in forum platforms and could expose sensitive data that might include personal information, business discussions, or other confidential material. The vulnerability is particularly concerning because it leverages legitimate forum functionality rather than requiring complex exploitation techniques, making it easily exploitable by both technical and non-technical attackers.
Security professionals should consider this vulnerability in the context of CWE-284 which addresses improper access control issues, and its relationship to ATT&CK technique T1078 which covers valid accounts and legitimate credentials. The vulnerability represents a classic case of insufficient authorization checks within application logic, where the plugin fails to properly enforce access control policies during routine user interactions. Mitigation strategies should include immediate plugin updates to versions that address the access control bypass, implementation of additional monitoring for unauthorized content access patterns, and review of all forum plugins for similar permission validation issues. Administrators should also consider implementing additional security controls such as enhanced logging of postbit interactions and regular security audits of forum plugin configurations to prevent similar vulnerabilities from being introduced through third-party components. The incident highlights the importance of thorough security testing for forum plugins and the need for robust access control validation in all user interaction pathways.