TinyMCE 4.x is vulnerable to several XSS vectors, which had been patched in later versions. Two of these have been identified as affecting "silverstripe/admin". Only Silverstripe CMS 4 is affected by this issue. It's not possible to upgrade Silverstripe CMS 4 to use a more recent release of TinyMCE without introducing breaking changes. Instead, the security patches that shipped in later releases of TinyMCE have been backported to the TinyMCE version bundled in "silverstripe/admin". Silverstripe CMS 5 is not affected by those vulnerabilities because it uses TinyMCE 6. You can find more information about the underlying vulnerabilities in those GitHub security advisories: - "GHSA-5h9g-x5rv-25wg Cross-site scripting vulnerability in TinyMCE" (https://github.com/advisories/GHSA-5h9g-x5rv-25wg) - "GHSA-w7jx-j77m-wp65 Cross-site scripting vulnerability in TinyMCE" (https://github.com/advisories/GHSA-w7jx-j77m-wp65)