CVE-2026-55247
criticalpriority · track · 0EPSS 0.004 · 38 %ileUSEPSS · scored 2026-10-28
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
Technical severity, 0–10. One row per scoring source.
base score 0–10 · higher = more severe · hover a vector to decode⚠ sources disagree · high–critical · 8.3–9.1
ssvc
A stakeholder decision — act, attend, or track — from exploitation and impact.
weaknesses
The CWE weakness classes this flaw belongs to.
affected products (2)
Products and version ranges known to be affected.
advisories (2)
Vendor and ecosystem advisories describing this.
- GHSA-r82h-mqw3-fc56plone.app.event vulnerable to denial of service via iCalendar import2026-08-28ghsa · osvUS
### 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.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 ### 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](mailto:security@plone.org). Thank you!
- PYSEC-2026-3883plone.app.event vulnerable to denial of service via iCalendar import2026-09-10vendor · osvUS
### 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.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 ### 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](mailto:security@plone.org). Thank you!
also known as (2)
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sources
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references (5) nvd
External citations — patches, advisories, analysis.
- 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/releases/tag/5.2.4
- https://github.com/plone/plone.app.event/releases/tag/6.0.1
- https://github.com/plone/plone.app.event/security/advisories/GHSA-r82h-mqw3-fc56
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