CVE-2021-43281 in MyBB
Summary
by MITRE • 11/04/2021
MyBB before 1.8.29 allows Remote Code Injection by an admin with the "Can manage settings?" permission. The Admin CP's Settings management module does not validate setting types correctly on insertion and update, making it possible to add settings of supported type "php" with PHP code, executed on Change Settings pages.
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Analysis
by VulDB Data Team • 11/10/2021
This vulnerability exists in MyBB versions prior to 1.8.29 and represents a critical remote code execution flaw that can be exploited by administrators possessing the "Can manage settings?" permission. The vulnerability stems from inadequate input validation within the Admin Control Panel's Settings management module, specifically in how the system handles setting type validation during both insertion and update operations. Attackers with administrative privileges can leverage this weakness to inject PHP code into settings that are configured to accept the "php" type, creating a persistent backdoor within the application's configuration system.
The technical flaw manifests through improper sanitization of user-supplied input within the administrative interface, allowing malicious code to be stored and subsequently executed when administrators navigate to the Change Settings pages. This represents a classic privilege escalation vulnerability where an attacker with limited administrative permissions can escalate their access to full system compromise. The vulnerability operates at the application level and directly impacts the integrity and confidentiality of the entire MyBB installation, as the injected PHP code executes with the privileges of the web server process.
The operational impact of this vulnerability is severe and far-reaching, as it provides attackers with complete control over the affected MyBB installation. Once exploited, adversaries can execute arbitrary commands on the server, potentially leading to data exfiltration, system compromise, or further lateral movement within the network. The vulnerability is particularly dangerous because it requires minimal privileges to exploit and can remain undetected for extended periods, as the injected code operates within legitimate administrative interfaces. This flaw can result in complete system compromise, data loss, and potential regulatory compliance violations for organizations using affected MyBB versions.
Organizations should immediately update to MyBB version 1.8.29 or later to remediate this vulnerability, as this release includes proper input validation and sanitization measures for administrative settings. Additionally, implementing network segmentation and monitoring for unusual administrative activities can help detect potential exploitation attempts. The vulnerability aligns with CWE-94, which describes weaknesses in the code that allow for arbitrary code execution, and maps to ATT&CK technique T1059.007 for execution through PHP code injection. Security teams should also conduct thorough audits of administrative user permissions and implement principle of least privilege practices to minimize potential impact if similar vulnerabilities are discovered in other systems.