CVE-2020-18166 in LAOBANCMS
Summary
by MITRE • 05/15/2021
Unrestricted File Upload in LAOBANCMS v2.0 allows remote attackers to upload arbitrary files by attaching a file with a ".jpg.php" extension to the component "admin/wenjian.php?wj=../templets/pc".
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Analysis
by VulDB Data Team • 05/16/2021
The vulnerability CVE-2020-18166 represents a critical unrestricted file upload flaw in LAOBANCMS v2.0 that exposes the application to remote code execution attacks. This vulnerability resides within the administrative component at admin/wenjian.php?wj=../templets/pc, where the system fails to properly validate file extensions and content, allowing malicious actors to bypass security controls and upload malicious files with deceptive extensions. The specific file extension ".jpg.php" demonstrates a common technique used to evade detection, as the server may process the file based on the latter part of the extension while the browser interprets it as an image file. This type of vulnerability falls under CWE-434, which specifically addresses unrestricted upload of files with dangerous types, and represents a significant weakness in the application's input validation and file handling mechanisms. The flaw enables attackers to upload PHP scripts disguised as image files, potentially gaining full control over the web server.
The technical implementation of this vulnerability exploits the lack of proper file validation within the file upload functionality. When an attacker uploads a file with the extension ".jpg.php", the application likely performs basic checks that only examine the file extension without validating the actual file content or implementing proper MIME type verification. This oversight allows the server to accept and process the file as a legitimate image while simultaneously executing any PHP code contained within it. The path traversal element in the URL parameter ../templets/pc suggests that the vulnerability may also involve directory traversal issues, potentially allowing attackers to upload files to arbitrary locations within the application's directory structure. This combination of unrestricted file upload and directory traversal creates a particularly dangerous attack vector that can lead to complete system compromise.
The operational impact of CVE-2020-18166 extends far beyond simple data theft, as it provides attackers with a pathway to achieve persistent access and execute arbitrary commands on the affected server. Once an attacker successfully uploads a malicious PHP file, they can leverage this access to establish reverse shells, install backdoors, or deploy additional malware. The vulnerability directly maps to ATT&CK technique T1105, which involves downloading and executing files, and can also facilitate lateral movement within networks through the establishment of persistent access points. Organizations running LAOBANCMS v2.0 become vulnerable to a wide range of attacks including data exfiltration, system compromise, and potential use as a launchpad for broader network infiltration. The vulnerability affects not only the immediate web application but can also compromise the underlying server infrastructure and potentially other systems connected to the same network.
Mitigation strategies for CVE-2020-18166 must address both the immediate vulnerability and implement comprehensive security controls to prevent similar issues. Organizations should immediately implement strict file extension validation that rejects all file types except explicitly allowed formats, while also implementing content-based validation using tools like file type detection libraries to verify actual file signatures. The application should enforce proper MIME type checking and avoid relying solely on file extensions for security decisions. Additionally, the upload directory should be configured with restricted permissions and separated from the web root to limit potential damage. Implementing Web Application Firewalls with rules specifically targeting file upload validation and employing regular security audits can help detect and prevent exploitation attempts. The solution should also include proper input sanitization and output encoding practices, as outlined in OWASP Top Ten security guidelines, to ensure that all user-provided data is properly validated before processing. Regular updates and patches for LAOBANCMS should be implemented immediately, as this vulnerability represents a known flaw that has likely been addressed in newer versions of the software.