CVE-2017-11127 in Bolt
Summary
by MITRE
Bolt CMS 3.2.14 allows stored XSS by uploading an SVG document with a "Content-Type: image/svg+xml" header.
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Analysis
by VulDB Data Team • 02/14/2025
Bolt CMS version 3.2.14 contains a critical stored cross-site scripting vulnerability that arises from improper handling of SVG file uploads. This vulnerability specifically affects the content management system's file upload validation mechanisms, where the application fails to adequately sanitize SVG content even when the file is properly identified with the correct MIME type header. The flaw exists in the application's media handling subsystem where uploaded files are stored and subsequently rendered without sufficient security controls to prevent malicious code execution. This vulnerability demonstrates a classic failure in input validation and output encoding practices that are fundamental to preventing XSS attacks.
The technical implementation of this vulnerability stems from the application's trust of the Content-Type header without performing additional validation of the actual file content. When an attacker uploads an SVG document with the proper MIME type header, the system accepts it as valid media content and stores it in the database. However, the system does not properly filter or escape SVG elements that may contain malicious JavaScript code or other harmful constructs. The stored SVG file can then be rendered in web browsers when accessed through the CMS interface, providing an execution environment for the embedded malicious code. This represents a failure in the principle of least privilege and proper input sanitization, where the application should treat all uploaded content as potentially malicious regardless of its declared type.
The operational impact of this vulnerability is significant as it allows attackers to persist malicious code within the CMS environment, potentially leading to complete system compromise. An attacker who gains access to upload capabilities can execute arbitrary JavaScript code in the context of other users' browsers, enabling session hijacking, data exfiltration, or further lateral movement within the network. The stored nature of the vulnerability means that the malicious code persists even after the initial upload, making it particularly dangerous for long-term compromise. This vulnerability directly relates to CWE-79 which describes improper neutralization of input during web output, and aligns with ATT&CK technique T1059.007 for command and scripting interpreter. The vulnerability can be exploited by attackers at the application level through the CMS upload functionality, potentially escalating to full system compromise if the CMS has elevated privileges or if users with administrative access interact with the malicious content.
Mitigation strategies should focus on implementing comprehensive input validation and output encoding controls for all uploaded content. The system should perform additional content validation beyond MIME type checking, including parsing SVG files to ensure they contain only safe elements and attributes. Implementing Content Security Policy headers, proper output encoding for all dynamic content, and restricting upload capabilities to authenticated users with appropriate privileges are essential defensive measures. Regular security auditing of file upload handlers and implementing automated tools to scan uploaded content for malicious patterns can help detect and prevent exploitation attempts. Organizations should also consider implementing web application firewalls to monitor and filter suspicious upload traffic, and establish proper access controls to limit who can upload files to the system. The vulnerability highlights the importance of defense in depth approaches where multiple layers of security controls work together to prevent exploitation.