CVE-2005-0269 in GNUBoard
Summary
by MITRE
The file extension check in GNUBoard 3.40 and earlier only verifies extensions that contain all lowercase letters, which allows remote attackers to upload arbitrary files via file extensions that include uppercase letters.
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Analysis
by VulDB Data Team • 07/06/2018
The vulnerability identified as CVE-2005-0269 represents a critical security flaw in GNUBoard versions 3.40 and earlier, specifically within the file extension validation mechanism. This weakness stems from an insufficient input validation approach that fails to properly sanitize file extensions during upload processes. The vulnerability is categorized under CWE-434, which addresses "Unrestricted Upload of File with Dangerous Type," highlighting the fundamental issue of inadequate file type verification that can lead to arbitrary code execution. The flaw manifests when the application performs a case-sensitive comparison against file extensions, allowing malicious actors to bypass security measures by using uppercase letters in their file extensions.
The technical implementation of this vulnerability exploits a fundamental flaw in the validation logic where the system only checks for lowercase extensions during file upload verification. When an attacker uploads a file with an uppercase extension such as ".PHP" instead of ".php", the system incorrectly accepts the file because it fails to recognize that ".PHP" represents the same file type as ".php" in terms of execution capabilities. This oversight occurs due to the application's failure to normalize the file extension to lowercase before validation, creating a pathway for attackers to execute malicious code through file uploads. The vulnerability directly relates to ATT&CK technique T1190, which involves exploiting weaknesses in file upload validation to gain unauthorized access and execute arbitrary code on the target system.
The operational impact of this vulnerability extends beyond simple file upload restrictions, creating potential pathways for complete system compromise. Attackers can leverage this flaw to upload malicious files such as web shells, backdoors, or other executable code that can be triggered through web requests. Once successfully uploaded, these files can provide attackers with persistent access to the server, enabling them to perform various malicious activities including data exfiltration, privilege escalation, and establishing footholds for further network penetration. The vulnerability is particularly dangerous in web applications where file uploads are common, as it can be exploited through various attack vectors including web interfaces, API endpoints, or file upload forms. The lack of proper extension normalization means that even administrators who might expect to be protected by standard security measures could be vulnerable to this type of attack, as the system fails to properly validate the actual file type regardless of case variations.
Mitigation strategies for CVE-2005-0269 require immediate implementation of proper file extension validation and normalization techniques. Organizations should ensure that all file extensions are converted to lowercase before validation occurs, preventing attackers from bypassing security measures through case variations. Additionally, comprehensive file type validation should be implemented using multiple approaches including MIME type checking, file content analysis, and whitelist-based validation of allowed extensions. The system should also employ proper file upload restrictions such as storing uploaded files outside the web root directory, implementing proper file permissions, and using secure file naming conventions to prevent predictable file paths. Regular security audits and code reviews should be conducted to identify similar validation flaws, and system administrators should ensure that all GNUBoard installations are updated to versions that address this vulnerability. The remediation process should also include implementing network-level protections such as web application firewalls that can detect and block suspicious file upload patterns, along with monitoring systems that can alert administrators to potential exploitation attempts.