CVE-2018-19508 in cmsimple
Summary
by MITRE
CMSimple 4.7.5 has XSS via an admin's upload of an SVG file at a ?userfiles&subdir=userfiles/images/flags/ URI.
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Analysis
by VulDB Data Team • 04/22/2020
The vulnerability identified as CVE-2018-19508 affects CMSimple version 4.7.5 and represents a cross-site scripting flaw that arises from improper handling of SVG file uploads within the administrative interface. This issue occurs when administrators upload SVG files to the specific directory path userfiles/images/flags/ which is accessible through the ?userfiles&subdir=userfiles/images/flags/ URI. The vulnerability stems from the application's failure to properly sanitize or validate SVG content before storing and serving these files, creating an avenue for malicious actors to inject arbitrary JavaScript code that executes in the context of other users' browsers.
The technical implementation of this vulnerability involves the manipulation of SVG files which can contain embedded JavaScript through various mechanisms such as script elements, event handlers, or external references. When an administrator uploads an SVG file containing malicious code, the application processes this file without adequate validation, allowing the malicious content to be stored in the designated userfiles directory. The vulnerability becomes exploitable when the SVG file is subsequently accessed through the web interface, as the browser renders the SVG content and executes any embedded JavaScript code within the context of the authenticated administrator's session.
The operational impact of this vulnerability is significant as it allows attackers to perform arbitrary actions on behalf of authenticated administrators. This includes but is not limited to stealing session cookies, performing unauthorized administrative actions, redirecting users to malicious sites, or exfiltrating sensitive information from the CMSimple installation. The attack requires only a single administrative upload of a malicious SVG file, making it particularly dangerous as it can be exploited without requiring complex initial access vectors. The vulnerability affects the confidentiality, integrity, and availability of the web application, potentially leading to complete system compromise.
Security mitigations for this vulnerability should focus on implementing proper input validation and sanitization of all uploaded files, particularly SVG content. The application should employ strict file type validation that rejects SVG files containing potentially dangerous elements or attributes, and implement comprehensive content sanitization that removes or neutralizes any embedded JavaScript code. Organizations should also consider implementing Content Security Policy headers to prevent execution of inline scripts, and regular security audits of uploaded content. This vulnerability aligns with CWE-79 which describes Cross-site Scripting flaws, and maps to ATT&CK technique T1059.007 for script execution through web shells or malicious uploads. The remediation process should include updating to a patched version of CMSimple, implementing file upload restrictions, and conducting comprehensive security testing to ensure no other similar vulnerabilities exist within the application's file handling mechanisms.