CVE-2023-5547 in Moodle
Summary
by MITRE • 11/09/2023
The course upload preview contained an XSS risk for users uploading unsafe data.
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Analysis
by VulDB Data Team • 05/18/2026
The vulnerability identified in the course upload preview functionality represents a cross-site scripting weakness that exposes users to potential security threats during data upload operations. This type of vulnerability falls under the CWE-79 category, which specifically addresses cross-site scripting flaws in web applications. The issue occurs when the system fails to properly sanitize or encode user-supplied input before rendering it in the preview interface, creating an avenue for malicious actors to inject harmful scripts that can execute in the context of other users' browsers.
The technical implementation flaw stems from insufficient input validation and output encoding mechanisms within the upload preview component. When users upload course materials containing malicious script code, the system processes this data without adequate sanitization before displaying it in the preview window. This allows attackers to craft specially formatted content that, when rendered in the preview, executes unintended JavaScript code in the browsers of other users who view the same content. The vulnerability is particularly concerning because it leverages legitimate user interactions with the preview functionality, making it more difficult to detect and prevent.
The operational impact of this vulnerability extends beyond simple data corruption or display issues. Attackers could potentially exploit this weakness to steal session cookies, perform unauthorized actions on behalf of users, or redirect victims to malicious websites. The risk is amplified when considering that course upload previews are typically accessible to multiple users within educational institutions, creating a broad attack surface. This vulnerability directly relates to ATT&CK technique T1566.001 which covers "Phishing: Spearphishing Attachment" and T1566.002 for "Phishing: Spearphishing Link" as attackers could use this vector to deliver malicious payloads through seemingly legitimate course materials.
Mitigation strategies should focus on implementing comprehensive input validation and output encoding mechanisms throughout the upload preview pipeline. The system must sanitize all user-supplied content using established libraries and frameworks designed to prevent XSS attacks, such as HTML escaping for display contexts. Additionally, content security policies should be enforced to restrict script execution and prevent unauthorized code injection. Regular security testing including dynamic application security testing and manual penetration testing should be conducted to identify similar vulnerabilities in other upload and preview functionalities. The implementation of proper access controls and user input restrictions will further reduce the attack surface and ensure that only authorized content is processed and displayed in preview environments.