plone.restapi: Stored XSS by spoofing mime type
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.restapito 9.15.6. - For Plone 6.2, upgrade
plone.restapito 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 software
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| Platform | Package | Vulnerable versions | Fixed in |
|---|---|---|---|
| Python (PyPI) | plone-restapi | < 9.15.6, >= 10.0.0, < 10.0.1 | 9.15.6, 10.0.1 |
References
- CVSS vector
CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:N/A:N- Weakness (CWE)
CWE-80- Platform
- Python (PyPI)
- Package
plone-restapi- Disclosed
- 17.07.2026
- Updated
- 11.10.2026 14:18
Sources and licenses
OSV / GitHub Advisory Database - GHSA-8rqh-vxpr-x77p - CC BY 4.0
Vulnerability history: plone-restapi
All published vulnerabilities of this package (Python (PyPI)), newest first. Shows whether this is a one-off slip or a package that needs watching.
- Total entries
- 3
- First → latest
- 01.2020 07.2026
- Without a fix
- 0
- Exploited in attacks
- 0
Severity breakdown
- High 1
- Medium 1
- Low 1
Disclosures per year
- 2020: 1
- 2021: 0
- 2022: 0
- 2023: 1
- 2024: 0
- 2025: 0
- 2026: 1
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plone.restapi: Stored XSS by spoofing mime type this entry
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