CVE-2019-9737 in Editor.md
Summary
by MITRE
Editor.md 1.5.0 has DOM-based XSS via vectors involving the '<EMBED SRC="data:image/svg+xml' substring.
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Analysis
by VulDB Data Team • 07/31/2023
The vulnerability CVE-2019-9737 represents a critical DOM-based cross-site scripting flaw discovered in Editor.md version 1.5.0, a popular open-source markdown editor. This vulnerability specifically exploits the editor's handling of embedded content through the '<EMBED SRC="data:image/svg+xml' substring pattern, which allows attackers to inject malicious scripts directly into the web application's DOM structure. The flaw exists within the editor's content rendering mechanism where user-provided input containing this specific SVG embedding pattern is not properly sanitized or escaped before being processed by the browser's DOM parser. This particular attack vector leverages the browser's native handling of embedded SVG content, bypassing traditional input validation measures that might only check for standard script tags or common XSS patterns.
The technical execution of this vulnerability occurs when an attacker crafts malicious input containing the '<EMBED SRC="data:image/svg+xml' substring followed by malicious JavaScript code within an SVG payload. When the Editor.md editor processes this content, the embedded SVG element gets rendered in the browser, and the embedded JavaScript code executes within the context of the vulnerable application's domain. This DOM-based XSS attack does not require server-side processing to be effective, as the malicious code is executed directly in the victim's browser session, making it particularly dangerous for web applications that rely on client-side rendering. The vulnerability falls under CWE-79 which specifically addresses Cross-Site Scripting, and more precisely aligns with CWE-937 which covers the weakness of using insecure methods in web applications. The attack chain typically involves an attacker first injecting the malicious SVG payload through a vulnerable input field, then tricking a victim into viewing the malicious content, whereupon the embedded JavaScript executes with the privileges of the victim's session.
The operational impact of CVE-2019-9737 extends beyond simple script execution, as it can enable attackers to perform session hijacking, steal sensitive user data, manipulate application functionality, and potentially escalate privileges within the affected web application. Since the vulnerability affects a widely-used markdown editor, it could compromise numerous web applications that integrate this component, particularly those that allow user-generated content or admin panels where markdown editing is permitted. The vulnerability creates a persistent threat vector that can be exploited across different user sessions, making it particularly dangerous for content management systems, forums, and collaborative editing platforms where multiple users interact with shared content. This type of vulnerability can also be leveraged as part of larger attack chains, potentially serving as a foothold for more sophisticated attacks such as credential theft or lateral movement within network environments, as outlined in the MITRE ATT&CK framework under technique T1566 for credential harvesting and T1071 for application layer protocol usage.
Organizations using Editor.md version 1.5.0 should immediately implement multiple layers of defense to mitigate this vulnerability. The most effective immediate remediation involves upgrading to a patched version of Editor.md where the vulnerable SVG handling has been properly addressed through input sanitization and proper escaping of embedded content. Additionally, implementing Content Security Policy (CSP) headers that restrict the execution of inline scripts and embedded content can provide an additional defensive layer. Web application firewalls should be configured to detect and block patterns matching the '<EMBED SRC="data:image/svg+xml' substring, and input validation should be strengthened to reject any content containing potentially dangerous embedded elements. Regular security assessments and automated vulnerability scanning should be implemented to identify similar patterns in other components of the web application stack. The mitigation strategy should also include user education about the risks of viewing untrusted content and implementing proper access controls to limit the impact of potential exploitation. Organizations should also consider implementing browser security features such as the sandbox attribute for embedded content and ensuring that all user-generated content is properly validated and sanitized before being rendered in the browser environment.