---
id: CVE-2026-55247
aliases:
  - GHSA-r82h-mqw3-fc56
  - PYSEC-2026-3883
title: plone.app.event vulnerable to denial of service via iCalendar import
summary: plone.app.event vulnerable to denial of service via iCalendar import
severity: critical
cvss: 9.1
cvssVector: 'CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:L/I:L/A:H'
vendor: plone-app-event
product: plone-app-event
ecosystem: pip
affected:
  - plone-app-event < 5.2.4
  - 'plone-app-event >= 6.0.0a1, < 6.0.1'
patched:
  - plone-app-event 5.2.4
  - plone-app-event 6.0.1
published: '2026-08-28'
updated: '2026-09-10'
sourceUpdated: '2026-09-10T12:25:52.689617832Z'
source: OSV
sourceUrl: 'https://osv.dev/vulnerability/GHSA-r82h-mqw3-fc56'
references:
  - url: >-
      https://github.com/plone/plone.app.event/security/advisories/GHSA-r82h-mqw3-fc56
  - url: >-
      https://github.com/plone/plone.app.event/commit/1e3c83c15a24d1a789cdb012593505bc5620e28e
  - url: >-
      https://github.com/plone/plone.app.event/commit/4de5eb3ea9e4f7f1781622e6d64fc086629d1437
  - url: 'https://github.com/plone/plone.app.event'
  - url: 'https://github.com/plone/plone.app.event/releases/tag/5.2.4'
  - url: 'https://github.com/plone/plone.app.event/releases/tag/6.0.1'
  - url: 'https://pypi.org/project/plone-app-event'
  - url: 'https://github.com/advisories/GHSA-r82h-mqw3-fc56'
  - url: 'https://nvd.nist.gov/vuln/detail/CVE-2026-55247'
tags:
  - osv
  - pip
  - nvd
  - ghsa
epss: 0.00441
epssPercentile: 0.35585
cwe:
  - CWE-400
ingestedAt: '2026-08-28T19:24:18.987Z'
---

## Overview

### 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!

## Affected packages

- `plone-app-event < 5.2.4`
- `plone-app-event >= 6.0.0a1, < 6.0.1`

## Remediation

Upgrade to a patched release:

- `plone-app-event 5.2.4`
- `plone-app-event 6.0.1`