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

MEDIUM

GHSA-8rqh-vxpr-x77p is a medium-severity (CVSS 4.3) vulnerability in plone-restapi. A fix is available for plone-restapi — see the affected versions and patch details below.

Published
Updated
Affected
2 pkgs
Patched
2 / 2
Exploits
None indexed
Exploitation data as of Jul 17, 2026 · OSV.dev, FIRST.org (EPSS)

Real-World Exposure

2 pkgs affected
🐍plone-restapi🐍plone-restapi

Real-time download stats are indexed for npm and PyPI packages. This vulnerability affects PyPI packages — download data is not available via public APIs for these ecosystems.

Description

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

2 total 2 fixed
EcosystemPackageVulnerable rangeFix
🐍PyPIplone-restapiall versions9.15.6pip install --upgrade 'plone-restapi==9.15.6'
🐍PyPIplone-restapi≥ 10.0.0&&< 10.0.110.0.1pip install --upgrade 'plone-restapi==10.0.1'

Detection & mitigation playbook

Open-source dependency

  1. Detect

    Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for plone-restapi, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.

  2. Fix

    Update plone-restapi to 9.15.6 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms GHSA-8rqh-vxpr-x77p is resolved across your whole dependency graph.

  3. Workarounds

    Escape or sanitise the affected output on the server side rather than relying on client-side filtering, and add a Content-Security-Policy that blocks inline script execution so injected markup cannot run even if it reaches the page.

Frequently Asked Questions

### 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="struc
O3 Security · Impact-Aware SCA

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plone.restapi: Stored XSS by spoofing mime type