CVE-2026-55247

plone.app.event vulnerable to denial of service via iCalendar import

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!

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.

Crafted input forces the application to consume excessive CPU, memory, or other resources, degrading or denying service. Typical impact: denial of service.

CVE-2026-55247 has a CVSS score of 9.1 (Critical). The vector is network-reachable, low privileges required, and no user interaction. A CVSS score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether this affects your application depends on whether the vulnerable code is present and reachable in your environment. A fixed version is available (5.2.4, 6.0.1); upgrading removes the vulnerable code path.

Kodem intelligence

Already deployed Kodem?

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

1. What is CVE-2026-55247? CVE-2026-55247 is a critical-severity uncontrolled resource consumption vulnerability in plone.app.event (pip), affecting versions < 5.2.4. It is fixed in 5.2.4, 6.0.1. Crafted input forces the application to consume excessive CPU, memory, or other resources, degrading or denying service.
2. How severe is CVE-2026-55247? CVE-2026-55247 has a CVSS score of 9.1 (Critical). This score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether it represents real risk in your environment depends on whether the vulnerable code is present and reachable.
3. Which versions of plone.app.event are affected by CVE-2026-55247? plone.app.event (pip) versions < 5.2.4 is affected.
4. Is there a fix for CVE-2026-55247? Yes. CVE-2026-55247 is fixed in 5.2.4, 6.0.1. Upgrade to this version or later.
5. Is CVE-2026-55247 exploitable, and should I be worried? Whether CVE-2026-55247 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
6. What actually determines whether CVE-2026-55247 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
7. How do I fix CVE-2026-55247?
   • Upgrade plone.app.event to 5.2.4 or later
   • Upgrade plone.app.event to 6.0.1 or later