CVE-2009-4449 in MyBB
Summary
by MITRE
Directory traversal vulnerability in MyBB (aka MyBulletinBoard) 1.4.10, and possibly earlier versions, when changing the user avatar from the gallery, allows remote authenticated users to determine the existence of files via directory traversal sequences in the avatar and possibly the gallery parameters, related to (1) admin/modules/user/users.php and (2) usercp.php.
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Analysis
by VulDB Data Team • 09/26/2025
The CVE-2009-4449 vulnerability represents a directory traversal flaw in MyBB version 1.4.10 and potentially earlier releases, specifically affecting the user avatar management functionality. This vulnerability occurs when authenticated users attempt to change their avatars from the gallery, creating a security risk that can be exploited by remote attackers who have valid user credentials. The flaw stems from insufficient input validation and sanitization within the avatar handling mechanisms, particularly in two key files: admin/modules/user/users.php and usercp.php. The vulnerability enables attackers to manipulate file paths through directory traversal sequences, allowing them to probe the server's file system structure and determine the existence of sensitive files.
The technical implementation of this vulnerability exploits the lack of proper parameter validation in the avatar and gallery parameters. When users select avatars from the gallery, the application fails to adequately sanitize user-supplied input, permitting attackers to inject traversal sequences such as ../ or ..\ into the file path parameters. This weakness specifically impacts the administrative user management module and the user control panel functionality, where the application processes avatar selection requests. The flaw operates by allowing malicious input to bypass normal file access controls, potentially exposing system files, configuration data, or other sensitive resources that should remain inaccessible to regular users.
The operational impact of CVE-2009-4449 extends beyond simple file enumeration, as it provides attackers with reconnaissance capabilities that can lead to more severe exploitation opportunities. While the immediate effect is file system traversal and existence checking, this vulnerability can serve as a stepping stone for attackers to identify sensitive files, configuration parameters, or system artifacts that may contain credentials, database connection strings, or other valuable information. The authenticated nature of the attack means that an attacker must first obtain valid user credentials, but this requirement does not significantly reduce the risk since legitimate users with access to the system could potentially be compromised through various means. The vulnerability affects the application's integrity by allowing unauthorized file system access and could potentially enable further exploitation paths including arbitrary file reading or even code execution depending on the server configuration.
Security mitigations for CVE-2009-4449 should focus on implementing robust input validation and sanitization mechanisms within the avatar handling code. Organizations should ensure that all user-supplied parameters undergo strict validation before being processed, particularly in file path operations. The fix requires implementing proper parameter sanitization to prevent directory traversal sequences from being processed, along with enforcing strict access controls that limit file operations to predefined directories. Additionally, implementing proper input encoding and output escaping techniques can prevent malicious traversal sequences from being interpreted as valid file paths. This vulnerability aligns with CWE-22, which describes improper limitation of a pathname to a restricted directory, and can be mapped to ATT&CK technique T1083, which covers file and directory discovery. The remediation approach should include thorough code review of file handling functions, implementation of whitelist-based validation for acceptable file paths, and ensuring that all file operations occur within designated safe directories to prevent unauthorized access to system resources.