Cross-site scripting vulnerability in TinyMCE
Impact
A cross-site scripting (XSS) vulnerability was discovered in the URL sanitization logic of the core parser. The vulnerability allowed arbitrary JavaScript execution when inserting a specially crafted piece of content into the editor using the clipboard or APIs. This impacts all users who are using TinyMCE 5.5.1 or lower.
Patches
This vulnerability has been patched in TinyMCE 5.6.0 by improved URL sanitization logic.
Workarounds
To work around this vulnerability, either:
- Upgrade to TinyMCE 5.6.0 or higher
- Manually sanitize
iframe,objectandembedURL attributes using a TinyMCE node filter. - Disable
iframe,object, andembedelements in your content using the invalid_elements setting.
Example: Sanitizing using a node filter
editor.parser.addNodeFilter('iframe,object,embed', function(nodes) {
nodes.forEach(function(node) {
if (node.attributes) {
node.attributes.forEach(function(attr) {
var name = attr.name;
var value = attr.value;
// Sanitize the attribute value here or remove it entirely
var sanitizedValue = ...;
node.attr(name, santizedValue);
});
}
});
});
Example: Using invalid_elements
invalid_elements: 'iframe,object,embed'
Acknowledgements
Tiny Technologies would like to thank Aaron Bishop at SecurityMetrics for discovering this vulnerability.
References
https://www.tiny.cloud/docs/release-notes/release-notes56/#securityfixes
For more information
If you have any questions or comments about this advisory:
- Open an issue in the TinyMCE repo
- Email us at infosec@tiny.cloud
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