CVE-2026-55247

Received Received - Intake

Resource Exhaustion in Plone.app.event via iCalendar Import

Publication date: 2026-08-28

Last updated on: 2026-08-28

Assigner: GitHub, Inc.

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.

CVSS Scores

EPSS Scores

Probability:
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Meta Information

Published

2026-08-28

Last Modified

2026-08-28

Generated

2026-08-29

AI Q&A

2026-08-29

EPSS Evaluated

N/A

NVD

CVE-2026-55247

EUVD

EUVD-2026-67868

Affected Vendors & Products

Vendor	Product	Version / Range
plone	app_event	to 6.0.1 (exc)

Helpful Resources

Exploitability

CWE

KEV

CWE ID	Description
CWE-400	The product does not properly control the allocation and maintenance of a limited resource.

Attack-Flow Graph

Executive Summary

This vulnerability affects the plone.app.event package in Plone, specifically versions prior to 5.2.4 and 6.0.1. It involves the iCalendar import feature which improperly handles calendar and event URLs, leading to potential Denial of Service (DoS), Server-Side Request Forgery (SSRF), and stored Cross-Site Scripting (XSS) attacks. A logged-in editor can exploit this to request internal network resources, exhaust server resources, or inject malicious scripts.

Detection Guidance

To detect this vulnerability, monitor for unusual network activity or resource exhaustion during iCalendar imports. Check Plone logs for failed imports or excessive event processing. Use commands like 'netstat -tuln' to detect unexpected network connections or 'ps aux' to monitor high CPU/memory usage during import operations.

Impact Analysis

If you are a user or administrator of a Plone site running an affected version, an attacker with editor privileges could take your site offline through resource exhaustion, access internal network resources or local files via SSRF, or inject malicious scripts that execute in other users' browsers via stored XSS. This could lead to data breaches, unauthorized access, or disruption of services.

Compliance Impact

This vulnerability could lead to violations of GDPR (data protection and privacy) and HIPAA (health information security) due to potential unauthorized access to sensitive data via SSRF or XSS, data breaches from script injection, and service disruptions affecting availability. Compliance requires immediate patching to mitigate these risks.

Mitigation Strategies

Upgrade plone.app.event to versions 5.2.4 or 6.0.1 or later to apply the security patches.
Restrict the 'plone.app.event: Import Ical' permission to the Manager role only as a temporary workaround.
Set MAXIMUM_ICAL_IMPORT_SIZE_BYTES to a lower value (e.g., 50000) and MAXIMUM_ICAL_IMPORT_EVENTS to a conservative number (e.g., 20) via environment variables.
Review and validate all event URLs in your Plone instance to remove any malicious or unsafe URLs.

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