---
title: "CVE-2026-55247: plone.app.event vulnerable to denial of service via iCalendar import"
url: https://erroneo.us/security/cve/CVE-2026-55247/
description: "CVE-2026-55247 (plone.app.event (PyPI)): plone.app.event provides the event content type for Plone. Prior to versions 5.2.4 and 6.0.1, the iCalendar import…"
type: vulnerability-record
section: "Security Digest"
date_published: 2026-08-28
date_modified: 2026-08-31
publisher: erroneo.us
author: erroneo.us Security Desk
cve: "CVE-2026-55247"
kev: false
cvss: 9.1
epss: 0.00441
license: All rights reserved. Quote with attribution and a link.
---

# CVE-2026-55247: plone.app.event vulnerable to denial of service via iCalendar import

**Signal:** Critical, preconditions apply. Severe if exploited, but exploitation needs conditions that may not apply to you. (Computed from CISA KEV, EPSS and CVSS; not an editorial verdict.)

## Should you act?

- No confirmed exploitation. It is not in CISA’s KEV catalog and CISA’s SSVC assessment records no known exploitation. That can change quickly after a public write-up; re-check if you are affected.
- EPSS 0.4% , percentile 37: FIRST’s model estimates a 0.4% chance of exploitation activity in the next 30 days, higher than 37% of all scored CVEs (low). EPSS is a probability, not a verdict.
- Needs an account (low (any account)). Exposure depends on who can log in.
- Only applies if your dependency tree includes plone.app.event (PyPI) < 5.2.4, fixed in 5.2.4 ; plone.app.event (PyPI) >= 6.0.0a1, < 6.0.1, fixed in 6.0.1 . Check your lockfile, including transitive dependencies.

## What it is

plone.app.event provides the event content type for Plone. Prior to versions 5.2.4 and 6.0.1, the iCalendar import in src/plone/app/event/ical/importer.py accepts insufficiently restricted calendar and event URLs, does not adequately bound downloaded bytes or imported events, and commits work per event. A logged-in editor can make the server request internal network resources or local calendar files, exhaust resources and take the site offline, and store a malicious event URL that executes script in another user's browser. The fix restricts accepted URLs, applies MAXIMUMICALIMPORTSIZEBYTES and MAXIMUMICALIMPORTEVENTS limits, uses transaction savepoints, and validates event URLs. This issue is fixed in versions 5.2.4 and 6.0.1.

## Affected packages

- PyPI `plone.app.event` < 5.2.4 → fixed: 5.2.4
- PyPI `plone.app.event` >= 6.0.0a1, < 6.0.1 → fixed: 6.0.1

## Affected products (CVE record)

- plone plone.app.event: < 5.2.4, >= 6.0.0, < 6.0.1

## Severity

- GitHub_M CVSS 3.1: 9.1 `CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:L/I:L/A:H`
- GitHub CVSS 3.1: 9.1 `CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:L/I:L/A:H`

## Exploitation

- CISA KEV: not listed (no confirmed in-the-wild exploitation known to CISA).
- CISA SSVC assessment: exploitation none , automatable no , technical impact partial .
- FIRST EPSS (model of 2026-10-21): 0.44% probability of exploitation activity in the next 30 days; percentile 37.

## Sources

- [GitHub Advisory GHSA-r82h-mqw3-fc56](https://github.com/advisories/GHSA-r82h-mqw3-fc56)
- [CVE.org record CVE-2026-55247](https://www.cve.org/CVERecord?id=CVE-2026-55247)
- [NVD entry CVE-2026-55247](https://nvd.nist.gov/vuln/detail/CVE-2026-55247)
- [github.com](https://github.com/plone/plone.app.event/security/advisories/GHSA-r82h-mqw3-fc56)
- [github.com](https://github.com/plone/plone.app.event/commit/1e3c83c15a24d1a789cdb012593505bc5620e28e)
- [github.com](https://github.com/plone/plone.app.event/commit/4de5eb3ea9e4f7f1781622e6d64fc086629d1437)
- [github.com](https://github.com/plone/plone.app.event/releases/tag/5.2.4)
- [github.com](https://github.com/plone/plone.app.event/releases/tag/6.0.1)

---
Source page: https://erroneo.us/security/cve/CVE-2026-55247/ · Security Digest: https://erroneo.us/security/ · More: https://erroneo.us/llms.txt