GHSA-8rqh-vxpr-x77p plone.restapi: Stored XSS by spoofing mime type

• PyPI plone.restapi: < 9.15.6 → fixed in 9.15.6 • PyPI plone.restapi: >= 10.0.0, < 10.0.1 → fixed in 10.0.1

Impact A stored XSS affecting RichText fields. RichTextValue.output returns the raw, unsanitized stored value whenever the stored mimeType equals the outputMimeType. Because the safe-HTML output type (`text/x-html-safe`) is the type that signifies "already sanitized", any value whose stored mimeType equals it bypasses the safe_html transform entirely on render. The transform itself is sound — it correctly strips `on*` event-handler attributes and `javascript:/data:` URIs; the defect is that it is never invoked for these values. The unsanitized value is then emitted via `tal:content="structure ..."`, which performs no escaping, so the payload executes in the viewer's browser. This can be a problem when a RichText field is wrongly defined in code with a `mimeType` and `outputMimeType` that are the same, or when the REST API is used to the same effect. This is the same vulnerability as reported in `plone.app.textfield`: https://github.com/plone/plone.app.textfield/security/advisories/GHSA-4r4f-gg25-rmg5 Patches The problem has been patched: • For Plone 6.0 and 6.2, upgrade `plone.restapi` to 9.15.6. • For Plone 6.2, upgrade `plone.restapi` to 10.0.1. This will prevent abusing the REST API to store wrong rich text values. This will not prevent XSS from rich text fields that already have wrong values. For that, you will need a patched `plone.app.textfield` version. See the `plone.app.textfield` advisory linked above for versions. Workarounds There is no known workaround.