SilverStripe through 4.6.0-rc1 has an XXE Vulnerability in CSSContentParser. A developer utility meant for parsing HTML within unit tests can be vulnerable to XML External Entity (XXE) attacks. When this developer utility is misused for purposes involving external or user submitted data in custom project code, it can lead to vulnerabilities such as XSS on HTML output rendered through this custom code. This is now mitigated by disabling external entities during parsing. (The correct CVE ID year is 2020 [CVE-2020-25817, not CVE-2021-25817]).
In SilverStripe through 4.5.0, a specific URL path configured by default through the silverstripe/framework module can be used to disclose the fact that a domain is hosting a Silverstripe application. There is no disclosure of the specific version. The functionality on this URL path is limited to execution in a CLI context, and is not known to present a vulnerability through web-based access. As a side-effect, this preconfigured path also blocks the creation of other resources on this path (e.g. a page).