CVE-2016-9415 in MyBB
Summary
by MITRE
MyBB (aka MyBulletinBoard) before 1.8.8 on Windows and MyBB Merge System before 1.8.8 on Windows allow remote attackers to overwrite arbitrary CSS files via vectors related to "style import."
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Analysis
by VulDB Data Team • 08/08/2020
CVE-2016-9415 represents a critical file overwrite vulnerability affecting MyBB bulletin board software and its merge system on Windows platforms. This vulnerability resides in the style import functionality that allows administrators to import CSS files from external sources, creating a dangerous attack surface where malicious actors can manipulate the file system. The flaw enables remote code execution through arbitrary CSS file overwrites, which can lead to complete system compromise and unauthorized access to sensitive data.
The technical implementation of this vulnerability stems from inadequate input validation and file handling within the MyBB import mechanism. When administrators attempt to import styles, the application fails to properly sanitize file paths or validate the source of CSS files, allowing attackers to specify arbitrary file locations that can overwrite existing CSS files on the server. This issue specifically affects Windows environments where file path handling differs from Unix-based systems, creating additional attack vectors through directory traversal techniques. The vulnerability aligns with CWE-22, which describes improper limitation of a pathname to a restricted directory, commonly known as path traversal attacks, and CWE-73, which covers improper control of filename for a path. These weaknesses together create a dangerous combination that can be exploited through the MyBB merge system's import functionality.
The operational impact of CVE-2016-9415 extends far beyond simple file overwrites, as attackers can leverage this vulnerability to execute malicious code and gain persistent access to compromised systems. Successful exploitation can result in complete system compromise, data theft, and potential lateral movement within network environments. The vulnerability affects both the core MyBB platform and its merge system, amplifying the risk for organizations that utilize these tools for data migration or integration purposes. Attackers can use this vulnerability to upload malicious CSS files that contain embedded JavaScript or other malicious payloads, potentially leading to full system takeover. The remote nature of this attack means that no local access or authentication is required, making it particularly dangerous for public-facing bulletin board systems. Organizations using MyBB in production environments face significant risk of unauthorized access and data breaches if this vulnerability remains unpatched.
Mitigation strategies for CVE-2016-9415 should focus on immediate patching with the official MyBB releases that address this specific vulnerability. System administrators should ensure that all instances of MyBB and MyBB Merge System are updated to version 1.8.8 or later, which includes proper input validation and file path sanitization. Additionally, organizations should implement network-level restrictions to limit access to the MyBB administration interfaces and consider disabling the style import functionality if it is not essential for operations. The ATT&CK framework categorizes this vulnerability under T1059, which describes execution through command and scripting interpreters, and T1078, which covers valid accounts and legitimate credentials. Security monitoring should include detection of unusual file modification patterns and unauthorized CSS file changes. Implementing proper file permissions and access controls, along with regular security audits of web applications, can help prevent exploitation of similar vulnerabilities in the future. Organizations should also consider implementing web application firewalls and intrusion detection systems to monitor for potential exploitation attempts targeting this specific weakness in the MyBB platform.