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Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting')


Severity Medium
Score 6.1/10


TinyMCE is an open-source rich text editor. A mutation cross-site scripting (mXSS) vulnerability was discovered in TinyMCE's core undo and redo functionality. When a carefully-crafted HTML snippet passes the XSS sanitization layer, it is manipulated as a string by internal trimming functions before being stored in the undo stack. If the HTML snippet is restored from the undo stack, the combination of the string manipulation and reparative parsing by either the browser's native DOMParser API(TinyMCE 6) or the SaxParser API(TinyMCE 5) mutates the HTML maliciously, allowing an XSS payload to be executed. This vulnerability has been patched by ensuring HTML is trimmed using node-level manipulation instead of string manipulation. Users are advised to upgrade. There are no known workarounds for this vulnerability. This vulnerability affects NPM-tinymce, PHP-tinymce/tinymce, and NuGe-TinyMCE packages versions prior to 5.10.8, 6.0.x prior to 6.7.1.

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CWE-79 - Cross Site Scripting

Cross-Site Scripting, commonly referred to as XSS, is the most dominant class of vulnerabilities. It allows an attacker to inject malicious code into a pregnable web application and victimize its users. The exploitation of such a weakness can cause severe issues such as account takeover, and sensitive data exfiltration. Because of the prevalence of XSS vulnerabilities and their high rate of exploitation, it has remained in the OWASP top 10 vulnerabilities for years.

Advisory Timeline

  • Published