CVE-2019-11231 in GetSimple
Summary
by MITRE
An issue was discovered in GetSimple CMS through 3.3.15. insufficient input sanitation in the theme-edit.php file allows upload of files with arbitrary content (PHP code, for example). This vulnerability is triggered by an authenticated user; however, authentication can be bypassed. According to the official documentation for installation step 10, an admin is required to upload all the files, including the .htaccess files, and run a health check. However, what is overlooked is that the Apache HTTP Server by default no longer enables the AllowOverride directive, leading to data/users/admin.xml password exposure. The passwords are hashed but this can be bypassed by starting with the data/other/authorization.xml API key. This allows one to target the session state, since they decided to roll their own implementation. The cookie_name is crafted information that can be leaked from the frontend (site name and version). If a someone leaks the API key and the admin username, then they can bypass authentication. To do so, they need to supply a cookie based on an SHA-1 computation of this known information. The vulnerability exists in the admin/theme-edit.php file. This file checks for forms submissions via POST requests, and for the csrf nonce. If the nonce sent is correct, then the file provided by the user is uploaded. There is a path traversal allowing write access outside the jailed themes directory root. Exploiting the traversal is not necessary because the .htaccess file is ignored. A contributing factor is that there isn't another check on the extension before saving the file, with the assumption that the parameter content is safe. This allows the creation of web accessible and executable files with arbitrary content.
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Analysis
by VulDB Data Team • 08/04/2025
The vulnerability identified in GetSimple CMS version 3.3.15 represents a critical security flaw that combines multiple exploitation vectors to enable arbitrary code execution. This issue resides in the admin/theme-edit.php file where insufficient input sanitization permits authenticated users to upload files containing malicious content such as PHP code. The vulnerability is particularly concerning because authentication can be bypassed through a combination of configuration weaknesses and implementation flaws that collectively undermine the CMS's security posture. The root cause stems from the improper handling of file uploads combined with weak session management and inadequate input validation mechanisms.
The technical exploitation pathway begins with the authentication bypass mechanism that leverages Apache configuration defaults. Modern Apache installations typically disable the AllowOverride directive, which inadvertently exposes administrative credentials stored in data/users/admin.xml. While passwords are hashed, the vulnerability extends to the data/other/authorization.xml file which contains API keys that can be used to target session state manipulation. This custom session implementation relies on cookie_name crafting based on publicly available information such as site name and version, making it vulnerable to information leakage attacks. The vulnerability is further exacerbated by the fact that the system's CSRF protection, while present, can be circumvented through careful manipulation of the upload process.
The core technical flaw manifests in the theme-edit.php file where the system accepts user-provided content without proper validation of file extensions or content type checking. The upload mechanism checks for POST requests and CSRF nonces but fails to validate the file extension or content before saving, assuming the content parameter is safe. This assumption leads to a path traversal vulnerability that allows writing files outside the intended themes directory, although the .htaccess file being ignored in the default configuration means the traversal isn't strictly necessary for successful exploitation. The vulnerability is classified as CWE-434: Unrestricted Upload of File with Dangerous Type, which directly relates to the lack of proper file type validation and content sanitization.
The operational impact of this vulnerability is severe as it enables remote code execution capabilities for attackers who can gain access to the system through the bypassed authentication mechanism. Once authenticated, attackers can upload malicious PHP files that become immediately executable within the web server context, potentially leading to complete system compromise. The vulnerability affects the entire GetSimple CMS ecosystem and can be exploited by attackers with minimal privileges to achieve high-impact outcomes including data exfiltration, system takeover, and persistence mechanisms. According to ATT&CK framework, this vulnerability maps to T1059.007: Command and Scripting Interpreter: PowerShell and T1566.001: Phishing: Spearphishing Attachment, as it enables both code execution and initial access through file upload mechanisms.
Mitigation strategies should focus on multiple layers of defense including immediate patching of the GetSimple CMS to version 3.3.16 or later where this vulnerability has been addressed. Network-level protections should implement strict file type validation and content inspection for all file upload operations, particularly in administrative interfaces. The Apache configuration should be reviewed to ensure proper AllowOverride settings and that sensitive files are properly protected. Session management should be strengthened through proper session token generation and validation, and the custom authentication implementation should be replaced with standardized security mechanisms. Additionally, administrators should implement proper monitoring and logging of file upload activities to detect suspicious behavior patterns that may indicate exploitation attempts. The vulnerability serves as a reminder of the importance of defense in depth and proper input validation in web applications, particularly in administrative interfaces where the potential for damage is highest.