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plone.app.textfield: Stored XSS by spoofing mime type

Moderate severity GitHub Reviewed Published Jun 5, 2026 in plone/plone.app.textfield • Updated Jul 17, 2026

Package

pip plone.app.textfield (pip)

Affected versions

< 2.0.2
>= 3.0.0, < 3.0.2
= 4.0.0

Patched versions

2.0.2
3.0.2
4.0.1

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.

Patches

The problem has been patched:

  • For Plone 6.0, upgrade plone.app.textfield to 2.0.2.
  • For Plone 6.1, upgrade plone.app.textfield to 3.0.2.
  • For Plone 6.2, upgrade plone.app.textfield to 4.0.1.

Workarounds

There is no known workaround.

References

@mauritsvanrees mauritsvanrees published to plone/plone.app.textfield Jun 5, 2026
Published to the GitHub Advisory Database Jul 17, 2026
Reviewed Jul 17, 2026
Last updated Jul 17, 2026

Severity

Moderate

CVSS overall score

This score calculates overall vulnerability severity from 0 to 10 and is based on the Common Vulnerability Scoring System (CVSS).
/ 10

CVSS v3 base metrics

Attack vector
Network
Attack complexity
Low
Privileges required
Low
User interaction
None
Scope
Unchanged
Confidentiality
Low
Integrity
None
Availability
None

CVSS v3 base metrics

Attack vector: More severe the more the remote (logically and physically) an attacker can be in order to exploit the vulnerability.
Attack complexity: More severe for the least complex attacks.
Privileges required: More severe if no privileges are required.
User interaction: More severe when no user interaction is required.
Scope: More severe when a scope change occurs, e.g. one vulnerable component impacts resources in components beyond its security scope.
Confidentiality: More severe when loss of data confidentiality is highest, measuring the level of data access available to an unauthorized user.
Integrity: More severe when loss of data integrity is the highest, measuring the consequence of data modification possible by an unauthorized user.
Availability: More severe when the loss of impacted component availability is highest.
CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:N/A:N

EPSS score

Weaknesses

Improper Neutralization of Script-Related HTML Tags in a Web Page (Basic XSS)

The product receives input from an upstream component, but it does not neutralize or incorrectly neutralizes special characters such as <, >, and & that could be interpreted as web-scripting elements when they are sent to a downstream component that processes web pages. Learn more on MITRE.

CVE ID

CVE-2026-54503

GHSA ID

GHSA-4r4f-gg25-rmg5

Source code

Credits

  • @gyst gyst Remediation developer
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