CVE-2021-24386 in WP SVG Images Plugin
Summary
by MITRE • 07/06/2021
The WP SVG images WordPress plugin before 3.4 did not sanitise the SVG files uploaded, which could allow low privilege users such as author+ to upload a malicious SVG and then perform XSS attacks by inducing another user to access the file directly. In v3.4, the plugin restricted such upload to editors and admin, with an option to also allow author to do so. The description of the plugin has also been updated with a security warning as upload of such content is intended.
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Analysis
by VulDB Data Team • 07/10/2021
The vulnerability CVE-2021-24386 affects the WP SVG Images WordPress plugin version 3.3 and earlier, representing a critical security flaw that enables cross-site scripting attacks through improper input sanitization of uploaded SVG files. This vulnerability specifically targets the plugin's handling of Scalable Vector Graphics format files, which are commonly used for web graphics and can contain embedded JavaScript code. The flaw allows users with author-level privileges or higher to upload malicious SVG files that contain malicious scripts, creating a persistent threat vector that can compromise other users who view these files. The vulnerability stems from inadequate validation and sanitization of file uploads, where the plugin fails to properly filter or escape potentially dangerous content within SVG files.
The technical implementation of this vulnerability occurs because the plugin does not adequately sanitize SVG content during the upload process, allowing malicious code to persist in the file system. SVG files can contain embedded javascript through various elements such as script tags, event handlers, or external references that execute when the file is rendered in a web browser. When low privilege users with author permissions upload such files, they can embed malicious payloads that execute in the context of other users' browsers when they access the SVG files. This creates a classic cross-site scripting scenario where the malicious code can steal session cookies, redirect users to malicious sites, or perform actions on behalf of authenticated users. The vulnerability aligns with CWE-79 - Improper Neutralization of Input During Web Page Generation, which specifically addresses the failure to properly sanitize user input that can lead to XSS attacks.
The operational impact of CVE-2021-24386 extends beyond simple code execution, as it enables attackers to establish persistent footholds within WordPress environments and potentially escalate privileges through user session hijacking. When users with lower privileges upload malicious SVG files, they can create a backdoor that remains active until the file is deleted or the plugin is updated. The vulnerability is particularly dangerous because SVG files are commonly used for logos, icons, and other graphical elements that are frequently displayed on websites, ensuring maximum exposure for the malicious payload. Attackers can craft SVG files that appear legitimate while containing hidden malicious code, making detection more difficult and increasing the likelihood of successful exploitation. This vulnerability also demonstrates poor privilege separation, as the plugin allowed too many user roles to upload potentially dangerous files without proper security controls.
The remediation for CVE-2021-24386 involved implementing proper input validation and sanitization mechanisms within the WP SVG Images plugin. Version 3.4 introduced role-based restrictions that limit SVG uploads to editors and administrators, with an optional configuration that allows authors to upload files while maintaining security awareness. This approach aligns with the principle of least privilege and follows security best practices outlined in the OWASP Top Ten security framework. The updated plugin also includes enhanced security warnings in its documentation, educating users about the risks associated with SVG file uploads and the importance of proper file validation. Additionally, the mitigation strategy includes implementing proper content security policies, using SVG sanitization libraries, and ensuring that all uploaded files undergo thorough validation before being stored or made accessible to other users. The vulnerability serves as a reminder of the critical importance of input validation and the potential consequences of failing to properly sanitize user-supplied content in web applications. Organizations should implement comprehensive security measures including regular security audits, proper privilege management, and continuous monitoring of plugin updates to prevent similar vulnerabilities from being exploited in their WordPress environments.