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Vulnerability · Published Aug 28, 2026 · Assigned by GitHub_M

CVE-2026-55247plone.app.event: Denial of service via iCalendar import

Critical 9.1

In plain English

A critical-severity uncontrolled resource consumption in plone.app.event from plone. There are no confirmed reports of exploitation so far. The chance it is exploited in the next 30 days is estimated at 0.4% (higher than 38% of all known vulnerabilities). Fixed versions are available - upgrade the affected package.

Severity (CVSS 3.1)9.1Critical
Exploit odds (30 days)0.4%top 61.5% of all CVEs
Exploited in the wildNo reportsCISA SSVC: none
Attack toolingNoneno public tooling known

Official description

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 MAXIMUM_ICAL_IMPORT_SIZE_BYTES and MAXIMUM_ICAL_IMPORT_EVENTS limits, uses transaction savepoints, and validates event URLs. This issue is fixed in versions 5.2.4 and 6.0.1.

Affected packages & fixed versions

EcosystemPackageFixed inAdvisory
PyPIplone-app-event5.2.4GHSA-r82h-mqw3-fc56
PyPIplone-app-event6.0.1GHSA-r82h-mqw3-fc56
PyPIplone-app-event5.2.4, 6.0.1PYSEC-2026-3883

Affected products (as reported)

VendorProductVersions
plone plone.app.event < 5.2.4>= 6.0.0, < 6.0.1

Weakness: CWE-400 · Vector: CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:L/I:L/A:H

References