Executive brief
TinyMCE is a popular rich-text editor embedded in web applications. A cross-site scripting vulnerability in its HTML parser allowed attackers to inject malicious JavaScript code when content was pasted into the editor or inserted via APIs, potentially compromising user sessions and stealing data from anyone using an unpatched version.
Technical details
The vulnerability is a cross-site scripting (XSS) flaw in the core HTML parser and sanitization logic. When specially crafted HTML content (specifically malformed iframe elements) was inserted into the editor via clipboard or programmatic APIs, the parser failed to properly sanitize the content, allowing arbitrary JavaScript execution. The attack requires user interaction (pasting content or triggering an API call with malicious payload) but no authentication. The issue was patched in TinyMCE 4.9.11 and 5.4.1 with improved HTML parsing and sanitization, and also by adding iframe to the special elements list in the parser schema.
Affected products
- Tiny Technologies TinyMCE 4.9.10 and earlier; 5.0.0 through 5.4.0
Timeline
- 2020-08-10: disclosed
- 2020-08-10: patched: Patched in TinyMCE 4.9.11 and 5.4.1
- 2020-07-04: other: Parsing fix merged in PR #5843