CVE-2021-3312 in OpenCms
Summary
by MITRE • 10/08/2021
An XML external entity (XXE) vulnerability in Alkacon OpenCms 11.0, 11.0.1 and 11.0.2 allows remote authenticated users with edit privileges to exfiltrate files from the server's file system by uploading a crafted SVG document.
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Analysis
by VulDB Data Team • 10/14/2021
The vulnerability CVE-2021-3312 represents a critical XML external entity (XXE) flaw discovered in Alkacon OpenCms versions 11.0, 11.0.1, and 11.0.2. This vulnerability falls under the CWE-611 category of Improper Restriction of XML External Entity Reference, which is a well-documented weakness in web applications that process XML data. The flaw specifically affects the SVG document handling functionality within the content management system, creating a pathway for malicious actors to exploit the system's XML parser. The vulnerability requires only authenticated access with edit privileges, making it particularly dangerous as it can be leveraged by users who already have legitimate access to the system but with elevated permissions.
The technical implementation of this vulnerability occurs when the OpenCms system processes SVG files that contain malicious XML entities. When an authenticated user uploads a crafted SVG document, the system's XML parser attempts to resolve external entities referenced within the SVG file. This processing occurs without proper validation or restriction of external entity references, allowing attackers to construct XML documents that can access the server's file system. The XXE attack vector enables the retrieval of arbitrary files from the server, potentially including configuration files, database credentials, application source code, or other sensitive data that may be accessible through the file system.
The operational impact of this vulnerability extends beyond simple information disclosure, as it provides attackers with the capability to escalate their privileges and potentially gain deeper access to the underlying system. The attack can be executed remotely by authenticated users who possess edit permissions, making it particularly concerning for organizations that grant broad editing rights to their content management system. The vulnerability essentially allows for server-side request forgery attacks where the XML parser acts as an intermediary to access local resources. This creates a significant risk for organizations that store sensitive data within their file systems, as the attacker can potentially access configuration files that may contain database connection strings, API keys, or other critical credentials. The attack can be further enhanced through parameter entity expansion, allowing for more sophisticated data exfiltration techniques.
Security mitigations for this vulnerability should focus on implementing proper XML parser configuration and input validation. Organizations should ensure that all XML parsers within the OpenCms system are configured to disable external entity resolution entirely, preventing any potential XXE attacks from succeeding. The recommended approach includes implementing strict XML schema validation and disabling DTD processing when parsing SVG files or any other XML content. Additionally, organizations should enforce the principle of least privilege by carefully reviewing user permissions and ensuring that only authorized personnel have edit privileges that could potentially exploit this vulnerability. The implementation of web application firewalls and security monitoring solutions can also help detect and prevent such attacks by monitoring for suspicious XML content patterns. This vulnerability aligns with ATT&CK technique T1059.007 for XML External Entity Processing and T1566 for Phishing with Malicious Attachments, as it enables attackers to leverage authenticated access to perform server-side file access operations. Organizations should also consider implementing automated vulnerability scanning tools that can detect similar XXE vulnerabilities in their XML processing components, as this type of flaw frequently appears in web applications that handle user-uploaded content and XML-based data formats.