Cross-site scripting vulnerability in TinyMCE
Impact
A cross-site scripting (XSS) vulnerability was discovered in the schema validation 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 editor APIs. This malicious content could then end up in content published outside the editor, if no server-side sanitization was performed. This impacts all users who are using TinyMCE 5.8.2 or lower.
Patches
This vulnerability has been patched in TinyMCE 5.9.0 by ensuring schema validation was still performed after unwrapping invalid elements.
Workarounds
To work around this vulnerability, either:
- Upgrade to TinyMCE 5.9.0 or higher
- Manually sanitize the content using the
BeforeSetContentevent (see below)
Example: Manually sanitize content
editor.on('BeforeSetContent', function(e) {
var sanitizedContent = ...; // Manually sanitize content here
e.content = sanitizedContent;
});Acknowledgements
Tiny Technologies would like to thank William Bowling for discovering this vulnerability.
References
https://www.tiny.cloud/docs/release-notes/release-notes59/#securityfixes
For more information
If you have any questions or comments about this advisory:
- Email us at infosec@tiny.cloud
- Open an issue in the TinyMCE repo
Affected software
Click a technology to see all vulnerabilities affecting it.
| Platform | Package | Vulnerable versions | Fixed in |
|---|---|---|---|
| Composer package | tinymce/tinymce | < 5.9.0 | 5.9.0 |
| npm package | tinymce | < 5.9.0 | 5.9.0 |
| .NET (NuGet) | TinyMCE | < 5.9.0 | 5.9.0 |
References
- CVSS vector
CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N- Weakness (CWE)
CWE-79- Platform
- Composer, npm, .NET (NuGet)
- Package
tinymce/tinymce, tinymce, TinyMCE- Disclosed
- 22.10.2021
- Updated
- 11.10.2026 11:23
Sources and licenses
OSV / GitHub Advisory Database - GHSA-5h9g-x5rv-25wg - CC BY 4.0
Vulnerability history: TinyMCE
All published vulnerabilities of this package (.NET (NuGet)), newest first. Shows whether this is a one-off slip or a package that needs watching.
- Total entries
- 15
- First → latest
- 01.2021 06.2026
- Without a fix
- 0
- Exploited in attacks
- 0
Severity breakdown
- High 4
- Medium 11
Disclosures per year
- 2021: 3
- 2022: 1
- 2023: 3
- 2024: 4
- 2025: 0
- 2026: 4
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