CVE-2023-1720 in Bitrix24
Summary
by MITRE • 11/01/2023
Lack of mime type response header in Bitrix24 22.0.300 allows authenticated remote attackers to execute arbitrary JavaScript code in the victim's browser, and possibly execute arbitrary PHP code on the server if the victim has administrator privilege, via uploading a crafted HTML file through /desktop_app/file.ajax.php?action=uploadfile.
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Analysis
by VulDB Data Team • 11/29/2023
The vulnerability identified as CVE-2023-1720 represents a critical security flaw in Bitrix24 version 22.0.300 that stems from insufficient validation of file upload operations within the desktop application framework. This weakness specifically manifests in the /desktop_app/file.ajax.php endpoint where the system fails to properly enforce mime type validation during file upload processes. The absence of proper content-type headers and file validation mechanisms creates an exploitable condition that allows authenticated attackers to bypass security controls and upload malicious files. The vulnerability operates under the principle of insecure file handling where the application accepts files without adequate verification of their actual content type, opening pathways for code execution attacks.
The technical exploitation of this vulnerability occurs through a carefully crafted HTML file upload process that leverages the file.ajax.php endpoint with the uploadfile action parameter. When an authenticated user uploads a malicious file, the system does not validate whether the uploaded file matches its declared mime type, allowing attackers to upload HTML files containing embedded JavaScript payloads. This flaw directly relates to CWE-434 which addresses insecure file upload handling, where applications fail to properly validate file types and content. The vulnerability enables a form of cross-site scripting attack that can be escalated to server-side code execution when targeting administrator accounts, as these users possess elevated privileges that allow the malicious code to operate with higher permissions.
The operational impact of this vulnerability extends beyond simple client-side script execution to potentially enable complete system compromise when administrators interact with malicious files. The attack vector requires authentication, meaning that an attacker must first obtain valid credentials to exploit this weakness, but once achieved, the potential for damage is significant. The vulnerability creates a persistent threat where malicious code can execute within the victim's browser context, potentially stealing session cookies, performing unauthorized actions, or serving as a stepping stone for further attacks. When the administrator uploads or accesses the malicious file, the PHP code execution capability becomes viable, allowing attackers to potentially gain remote command execution privileges on the server. This escalation path aligns with ATT&CK technique T1059.007 which covers JavaScript and VBScript execution, and can be extended to T1078 for legitimate credentials usage and T1566 for phishing or social engineering.
Mitigation strategies for CVE-2023-1720 should focus on implementing comprehensive file validation mechanisms and restricting upload capabilities for sensitive user accounts. Organizations should enforce strict mime type validation on all file uploads through the affected endpoint, ensuring that files are verified against their declared content type before processing. The system should implement proper file extension filtering and content inspection to prevent HTML files from being executed in contexts where they could pose security risks. Additionally, administrators should be restricted from uploading files to directories where they could execute code, and the principle of least privilege should be enforced through role-based access controls. Network-level protections such as web application firewalls can help detect and block malicious upload attempts, while regular security audits and penetration testing should be conducted to identify similar vulnerabilities in the application stack. The fix should include proper input sanitization, content-type header enforcement, and comprehensive file validation that prevents the execution of potentially malicious code through file upload mechanisms.