CVE-2021-39136 in baserCMS
Summary
by MITRE • 08/25/2021
baserCMS is an open source content management system with a focus on Japanese language support. In affected versions there is a cross-site scripting vulnerability in the file upload function of the management system of baserCMS. Users are advised to update as soon as possible. No workaround are available to mitigate this issue.
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Analysis
by VulDB Data Team • 08/29/2021
The vulnerability CVE-2021-39136 represents a critical cross-site scripting flaw within baserCMS, a popular open source content management system designed primarily for Japanese language environments. This vulnerability specifically targets the file upload functionality of the administrative interface, making it particularly dangerous as it allows attackers to exploit the management system's upload capabilities to inject malicious scripts. The issue affects versions of baserCMS where proper input validation and output sanitization mechanisms are insufficiently implemented in the file handling components, creating an attack surface that can be leveraged by malicious actors to compromise the system.
The technical implementation of this vulnerability stems from inadequate sanitization of file names and metadata during the upload process. When administrators or authorized users interact with the file upload function, the system fails to properly validate or escape special characters that could be interpreted as HTML or JavaScript code. This weakness allows attackers to upload files with malicious payloads embedded in their names or metadata, which can then be executed when the file information is displayed within the management interface. The vulnerability operates under CWE-79 which specifically addresses cross-site scripting flaws, and aligns with ATT&CK technique T1203 which involves exploiting web application vulnerabilities to gain unauthorized access. The flaw demonstrates poor input validation practices that directly violate secure coding principles and security best practices for web application development.
The operational impact of this vulnerability extends beyond simple script execution, as it can enable attackers to perform various malicious activities within the compromised system. Once an attacker successfully exploits this vulnerability, they can potentially steal session cookies, redirect users to malicious sites, deface the content management system, or even escalate privileges within the administrative environment. The vulnerability's presence in the management system's file upload function means that any user with access to this functionality could become a vector for broader attacks on the organization's web infrastructure. This creates a significant risk for organizations relying on baserCMS, as the compromise of the management system can lead to complete system takeover, data exfiltration, and potential lateral movement within network environments where the CMS is deployed. The lack of available workarounds compounds the severity, as organizations cannot implement temporary mitigations while awaiting the official patch release.
Organizations using affected versions of baserCMS should immediately prioritize the application of security updates provided by the software vendor to address this vulnerability. The recommended mitigation strategy involves upgrading to the patched version of baserCMS that implements proper input validation and output encoding mechanisms for file upload operations. Security teams should also conduct comprehensive assessments of their baserCMS installations to identify any potential exploitation attempts and monitor web application logs for suspicious activities related to file uploads. Additionally, implementing network-level protections such as web application firewalls and restricting administrative access to trusted IP ranges can provide additional defense-in-depth measures. The vulnerability serves as a reminder of the critical importance of regular security updates and proper input validation in web applications, particularly those handling user-supplied data through file upload mechanisms. Organizations should also consider implementing automated vulnerability scanning tools to detect similar issues in other web applications within their environment, as the underlying principles of this vulnerability can be found in various other systems that fail to properly sanitize user inputs.