CVE-2023-41362 in MyBB
Summary
by MITRE • 08/29/2023
MyBB before 1.8.36 allows Code Injection by users with certain high privileges. Templates in Admin CP intentionally use eval, and there was some validation of the input to eval, but type juggling interfered with this when using PCRE within PHP.
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Analysis
by VulDB Data Team • 09/22/2023
CVE-2023-41362 represents a critical code injection vulnerability affecting MyBB versions prior to 1.8.36 that demonstrates how improper input validation combined with PHP's type juggling capabilities can create dangerous security flaws. This vulnerability specifically targets the Admin Control Panel where administrators can modify templates, creating a path for privilege escalation attacks. The flaw exists because MyBB's template system intentionally employs the eval() function to process user-supplied template data, which is a well-known security anti-pattern that should be avoided in production systems. The vulnerability stems from insufficient input sanitization mechanisms that fail to properly validate template content before execution.
The technical exploitation occurs through a combination of PHP's type juggling behavior and PCRE (Perl Compatible Regular Expressions) processing within the validation layer. When attackers craft malicious template content that exploits type coercion vulnerabilities in PHP's comparison operations, they can bypass the intended validation checks that were designed to prevent code injection. This type juggling vulnerability allows attackers to manipulate input data in ways that cause the validation logic to incorrectly accept malicious payloads, effectively rendering the security controls useless. The issue is particularly dangerous because it affects users with high privileges who have access to the Admin CP, enabling them to execute arbitrary code on the server with the privileges of the web application.
The operational impact of this vulnerability extends far beyond simple code execution, as it provides attackers with complete control over the affected MyBB installation. Once exploited, attackers can modify or delete content, access sensitive user data, escalate privileges further within the application, and potentially use the compromised system as a launch point for broader network attacks. The vulnerability's presence in the Admin CP means that even a single compromised administrator account could result in complete system compromise, making it particularly dangerous for organizations relying on MyBB for community forums or content management. This flaw directly violates the principle of least privilege and demonstrates how improper input handling in high-privilege areas can create catastrophic security implications.
Organizations should immediately update to MyBB 1.8.36 or later versions to remediate this vulnerability, as the patch addresses the core issue of inadequate input validation and the problematic use of eval() within the template processing system. System administrators should implement additional monitoring for unusual template modifications and consider implementing web application firewalls to detect and block malicious template content. The vulnerability aligns with CWE-94 (Improper Control of Generation of Code) and CWE-74 (Improper Neutralization of Special Elements in Output Used by a Downstream Component) and maps to ATT&CK techniques including T1059.001 (Command and Scripting Interpreter: PowerShell) and T1078 (Valid Accounts) as attackers may leverage this vulnerability to establish persistent access. Security teams should also review all custom templates and modifications to ensure no additional attack vectors have been introduced through custom code that might interact with the vulnerable template system.