CVE-2021-41279 in BaserCMS
Summary
by MITRE • 11/26/2021
BaserCMS is an open source content management system with a focus on Japanese language support. In affected versions users with upload privilege may upload crafted zip files capable of path traversal on the host operating system. This is a vulnerability that needs to be addressed when the management system is used by an unspecified number of users. If you are eligible, please update to the new version as soon as possible.
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Analysis
by VulDB Data Team • 12/02/2021
CVE-2021-41279 represents a critical path traversal vulnerability within BaserCMS, a popular open source content management system designed primarily for Japanese language environments. This vulnerability specifically targets the file upload functionality and exploits a flaw in how the system handles zip file extraction processes. The vulnerability allows authenticated users with upload privileges to craft malicious zip archives that can execute arbitrary file operations on the host operating system, potentially leading to complete system compromise.
The technical implementation of this vulnerability stems from inadequate input validation and sanitization during the zip file processing phase. When users with upload permissions submit crafted zip files, the system fails to properly validate the archive contents and directory structure, enabling attackers to manipulate the extraction path through directory traversal sequences. This flaw operates at the file system level, allowing malicious actors to write files to arbitrary locations on the server, potentially overwriting critical system files or establishing persistent backdoors. The vulnerability is particularly dangerous because it leverages legitimate upload functionality, making it harder to detect through traditional security monitoring mechanisms.
The operational impact of this vulnerability extends beyond simple privilege escalation, as it can enable attackers to gain full control over the affected server. Successful exploitation could result in data exfiltration, system compromise, service disruption, and potential lateral movement within network environments where BaserCMS is deployed. Given that BaserCMS is commonly used in business and government environments, the potential for sensitive data exposure or regulatory compliance violations is significant. The unspecified number of users mentioned in the advisory suggests that organizations may have multiple administrators or contributors with upload privileges, increasing the attack surface and likelihood of exploitation.
Organizations should immediately implement multiple layers of defense to mitigate this vulnerability. The primary and most critical mitigation is to upgrade to the patched version of BaserCMS as soon as possible, as this addresses the root cause through proper input validation and secure file extraction mechanisms. Additionally, implementing strict file type validation, limiting upload privileges to only essential personnel, and deploying web application firewalls with signature-based detection capabilities can provide additional protection. Security monitoring should include detection of unusual file upload activities and directory traversal patterns, while regular security audits should verify that no malicious files have been successfully uploaded through this vulnerability. This vulnerability aligns with CWE-22 Path Traversal and maps to ATT&CK technique T1059 Command and Scripting Interpreter, demonstrating how path traversal can lead to command execution and system compromise.