---
id: GHSA-8rqh-vxpr-x77p
title: 'plone.restapi: Stored XSS by spoofing mime type'
summary: 'plone.restapi: Stored XSS by spoofing mime type'
severity: medium
cvss: 4.3
cvssVector: 'CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:N/A:N'
vendor: plone-restapi
product: plone-restapi
ecosystem: pip
affected:
  - plone-restapi < 9.15.6
  - 'plone-restapi >= 10.0.0, < 10.0.1'
patched:
  - plone-restapi 9.15.6
  - plone-restapi 10.0.1
published: '2026-07-17'
updated: '2026-07-17'
source: OSV
sourceUrl: 'https://osv.dev/vulnerability/GHSA-8rqh-vxpr-x77p'
references:
  - url: >-
      https://github.com/plone/plone.app.textfield/security/advisories/GHSA-4r4f-gg25-rmg5
  - url: >-
      https://github.com/plone/plone.restapi/security/advisories/GHSA-8rqh-vxpr-x77p
  - url: 'https://github.com/plone/plone.restapi'
tags:
  - osv
  - pip
ingestedAt: '2026-07-17T19:00:50.704Z'
---

## Overview

### 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.

## Affected packages

- `plone-restapi < 9.15.6`
- `plone-restapi >= 10.0.0, < 10.0.1`

## Remediation

Upgrade to a patched release:

- `plone-restapi 9.15.6`
- `plone-restapi 10.0.1`