CVE-2018-7265 in Shimmie
Summary
by MITRE
Shimmie 2 2.6.0 allows an attacker to upload a crafted SVG file that enables stored XSS.
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Analysis
by VulDB Data Team • 02/08/2023
The vulnerability CVE-2018-7265 affects Shimmie 2 version 2.6.0 and represents a critical security flaw that enables stored cross-site scripting attacks through crafted SVG file uploads. This vulnerability resides in the image handling and processing functionality of the web application, where user-uploaded files are not properly sanitized or validated before being stored and served to other users. The issue specifically targets the SVG (Scalable Vector Graphics) file format which is commonly used for web graphics and is often processed without adequate security measures due to its XML-based nature. When an attacker uploads a malicious SVG file, the application fails to properly validate or sanitize the content, allowing malicious JavaScript code embedded within the SVG to be executed in the context of other users who view the uploaded image.
The technical implementation of this vulnerability stems from improper input validation and sanitization within the file upload processing pipeline. SVG files contain XML elements that can include embedded script tags, event handlers, and other potentially dangerous constructs that can be exploited to execute arbitrary code in web browsers. The vulnerability allows attackers to store malicious code within the application's database or file system, making it persistent and capable of affecting multiple users who access the vulnerable content. This stored XSS attack vector operates through the principle that when other users browse to pages containing the malicious SVG file, their browsers execute the embedded JavaScript code, potentially stealing session cookies, redirecting to malicious sites, or performing unauthorized actions on behalf of the victims.
The operational impact of CVE-2018-7265 extends beyond simple script execution, as it can enable sophisticated attack chains that compromise user sessions and potentially lead to full system compromise. Attackers can leverage this vulnerability to perform session hijacking, steal sensitive user information, inject malicious content into web pages, or redirect users to phishing sites that appear legitimate. The stored nature of the vulnerability means that the malicious payload persists even after the initial upload, making it particularly dangerous for content management systems where users frequently upload media files. This vulnerability directly maps to CWE-79 which describes Cross-Site Scripting flaws, and aligns with ATT&CK techniques related to code injection and credential access through web-based attacks. The vulnerability demonstrates a failure in the application's defense-in-depth principles, as it should have implemented multiple layers of validation including file type checking, content sanitization, and proper output encoding before serving any user-uploaded content to other users.
Mitigation strategies for CVE-2018-7265 should include immediate patching of the Shimmie 2 application to version 2.6.1 or later where the vulnerability has been addressed. Organizations should implement comprehensive file upload validation mechanisms that reject or sanitize SVG files containing potentially dangerous elements such as script tags, event handlers, or external references. The application should employ strict content type validation, implement proper file extension checking, and utilize dedicated SVG sanitization libraries that remove or neutralize malicious content while preserving legitimate graphic functionality. Additional protective measures include implementing Content Security Policy headers to prevent script execution, using proper output encoding when displaying user-generated content, and conducting regular security audits of file upload handlers. Security teams should also consider implementing web application firewalls that can detect and block suspicious SVG file patterns, and establish monitoring procedures to detect unauthorized file uploads that could indicate exploitation attempts. The vulnerability highlights the critical importance of validating and sanitizing all user-supplied content, particularly in web applications that handle multimedia files, and demonstrates how seemingly benign file formats can become attack vectors when not properly secured.