plone.app.event vulnerable to denial of service via iCalendar import
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.event6.0.1 - For Plone 6.1: upgrade to
plone.app.event5.2.4 - For Plone 6.0: upgrade to
plone.app.event5.2.4
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. Thank you!
Affected software
Click a technology to see all vulnerabilities affecting it.
| Platform | Package | Vulnerable versions | Fixed in |
|---|---|---|---|
| Python (PyPI) | plone-app-event | < 5.2.4, >= 6.0.0a1, < 6.0.1 | 5.2.4, 6.0.1 |
References
- https://github.com/plone/plone.app.event/security/advisories/GHSA-r82h-mqw3-fc56
- https://github.com/plone/plone.app.event/commit/1e3c83c15a24d1a789cdb012593505bc5620e28e
- https://github.com/plone/plone.app.event/commit/4de5eb3ea9e4f7f1781622e6d64fc086629d1437
- https://github.com/plone/plone.app.event
- https://github.com/plone/plone.app.event/releases/tag/5.2.4
- https://github.com/plone/plone.app.event/releases/tag/6.0.1
- https://pypi.org/project/plone-app-event
- https://github.com/advisories/GHSA-r82h-mqw3-fc56
- https://nvd.nist.gov/vuln/detail/CVE-2026-55247
- CVSS vector
CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:L/I:L/A:H- Weakness (CWE)
CWE-400- Platform
- Python (PyPI)
- Package
plone-app-event- Disclosed
- 28.08.2026
- Updated
- 11.10.2026 15:18
Sources and licenses
OSV / GitHub Advisory Database - PYSEC-2026-3883 - PyPA Advisory Database; CC BY 4.0
OSV / GitHub Advisory Database - GHSA-r82h-mqw3-fc56 - CC BY 4.0
Vulnerability history: plone-app-event
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
- 4
- First → latest
- 12.2020 08.2026
- Without a fix
- 0
- Exploited in attacks
- 0
Severity breakdown
- Critical 1
- High 3
Disclosures per year
- 2020: 3
- 2021: 0
- 2022: 0
- 2023: 0
- 2024: 0
- 2025: 0
- 2026: 1
-
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