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CVE-2026-55247 — Vulnerability in plone-app-event — CVE Details

CRITICAL

plone.app.event vulnerable to denial of service via iCalendar import

Published August 28, 2026Updated September 10, 2026Source: osv

Summary

### Impact By abusing the iCalendar import functionality, a logged-in editor could take the whole site offline, make the server reach into the internal network and read calendar files off disk (SSRF), and store XSS. ### Patches The problem has been patched in `plone.app.event`. * For Plone 6.2: upgrade to `plone.app.event` 6.0.1 * For Plone 6.1: upgrade to `plone.app.event` 5.2.4 * For Plone 6.0: upgrade to `plone.app.event` 5.2.4 ### Workarounds In the site root, go to the Security tab of the Zope Management Interface (`manage_access`), look for the "plone.app.event: Import Ical" permission, and grant this only to the Manager role. Then only users with the Manager role can use the ical import form. There is no workaround for the stored XSS in the URL field of events. The vulnerabilities were discovered by Timothy Dudley and responsibly reported to the [Plone Security Team](mailto:security@plone.org). Thank you!

Advisory Timeline

  • First published August 28, 2026 (45 days ago).
  • Last revised September 10, 2026 — 13 days after initial publication.

Remediation

Upgrade to the fixed version using your package manager.

pip
Update plone-app-event to 6.0.1 or later
pip install "plone-app-event>=6.0.1"
pip
Update plone-app-event to 5.2.4 or later
pip install "plone-app-event>=5.2.4"

After upgrading, run your dependency scanner again to confirm the vulnerability is resolved.

Affected Packages (2)

Affects 1 ecosystem: pypi (1).

PackageEcosystemAffectedFixed In
plone-app-event
pypi
6.0.0, 6.0.0a1, 6.0.0a26.0.1
plone-app-event
pypi
1.0, 1.0.1, 1.0.2, 1.0.3 (+121 more)5.2.4

Vulnerability Classification

Common Weakness Enumeration (CWE) identifiers for this vulnerability type.

  • CWE-400
    Uncontrolled Resource ConsumptionMITRE

CVSS Score Breakdown

What the CVSS (Common Vulnerability Scoring System) 9.1 score means for each attack dimension.

Attack Vector
Network
Attack Complexity
Low
Privileges Required
Low
User Interaction
None
Scope
Changed
Confidentiality
Low
Integrity
Low
Availability
High

CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:L/I:L/A:H

References

Frequently Asked Questions

What is CVE-2026-55247?
plone.app.event vulnerable to denial of service via iCalendar import This vulnerability has been assigned a severity rating of CRITICAL (CVSS score: 9.1/10).
How do I check if my project is affected by CVE-2026-55247?
CVE-2026-55247 affects plone-app-event. Use GeekWala's free vulnerability scanner to check your dependencies against CVE-2026-55247 and 200,000+ other known vulnerabilities.

Severity & Exploitability

CVSS Score
9.1

Exploitation is straightforward and causes maximum impact. Patch immediately.

Also Known As

GHSA-r82h-mqw3-fc56
PYSEC-2026-3883

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