CVE-2026-55247
plone.app.event: Denial of service via iCalendar import
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.
Attack profile
How easy it is to exploit
- Attack vector
- Network
- Complexity
- Low
- Privileges needed
- Low
- User interaction
- None
What an attacker can affect
- Confidentiality
- Low
- Integrity
- Low
- Availability
- High
Exploit likelihood
What each source reports
CVE List Score used
plone.app.event: Denial of service via iCalendar import
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.
- Record
CVE-2026-55247- CVSS 3.1
- 9.1 Critical
CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:L/I:L/A:H - Weakness
- CWE-400
- Updated
- 2026-11-02
EUVDEUVD-2026-67868
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.
- Record
EUVD-2026-67868- CVSS 3.1
- 9.1 Critical
CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:L/I:L/A:H - Updated
- 2026-11-02
GitHub AdvisoriesGHSA-r82h-mqw3-fc56
plone.app.event vulnerable to denial of service via iCalendar import
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.event6.0.1 - For Plone 6.1: upgrade to
plone.app.event5.2.4 - For Plone 6.0: upgrade to
plone.app.event5.2.4
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. Thank you!
- Record
GHSA-r82h-mqw3-fc56- CVSS 3.1
- 9.1 Critical
CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:L/I:L/A:H - Weakness
- CWE-400
- Updated
- 2026-11-02
NVD
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.
- Record
CVE-2026-55247- CVSS 3.1
- 9.1 Critical
CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:L/I:L/A:H - Weakness
- CWE-400
- Updated
- 2026-11-02
OSV
plone.app.event: Denial of service via iCalendar import
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.
- Record
CVE-2026-55247- CVSS 3.1
- 9.1 Critical
CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:L/I:L/A:H - Weakness
- CWE-400
- Updated
- 2026-11-02
OSVGHSA-r82h-mqw3-fc56
plone.app.event vulnerable to denial of service via iCalendar import
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.event6.0.1 - For Plone 6.1: upgrade to
plone.app.event5.2.4 - For Plone 6.0: upgrade to
plone.app.event5.2.4
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. Thank you!
- Record
GHSA-r82h-mqw3-fc56- CVSS 3.1
- 9.1 Critical
CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:L/I:L/A:H - Weakness
- CWE-400
- Updated
- 2026-11-02
OSVPYSEC-2026-3883
plone.app.event vulnerable to denial of service via iCalendar import
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.event6.0.1 - For Plone 6.1: upgrade to
plone.app.event5.2.4 - For Plone 6.0: upgrade to
plone.app.event5.2.4
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. Thank you!
- Record
PYSEC-2026-3883- CVSS 3.1
- 9.1 Critical
CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:L/I:L/A:H - Updated
- 2026-11-02
Affected products
Affected packages
| Package | Affected | Fixed |
|---|---|---|
plone-app-eventPyPI |
before 5.2.4 | 5.2.4 |
plone-app-eventPyPI |
6.0.0a1 up to 6.0.1 | 6.0.1 |
plone-app-eventPyPI |
before 5.2.4, plus listed versions 1.01.0.11.0.21.0.31.0.4 Show 45 moreShow less1.0.51.0.61.0a11.0a21.0b11.0b21.0b31.0b41.0b51.0b61.0b71.0b81.0rc11.0rc21.0rc31.11.1.11.1.101.1.111.1.121.1.131.1.21.1.31.1.41.1.51.1.61.1.71.1.81.1.a11.1b11.21.2.11.2.21.2.31.2.41.2.51.2.61.2.72.02.0.12.0.102.0.112.0.122.0.132.0.14 |
5.2.4 |
plone-app-eventPyPI |
6.0.0a1 up to 6.0.1, plus listed versions 6.0.06.0.0a2 |
6.0.1 |
plone-app-eventPyPI |
before 5.2.4, 6.0.0a1 up to 6.0.1, plus listed versions 1.01.0.11.0.21.0.31.0.4 Show 45 moreShow less1.0.51.0.61.0a11.0a21.0b11.0b21.0b31.0b41.0b51.0b61.0b71.0b81.0rc11.0rc21.0rc31.11.1.11.1.101.1.111.1.121.1.131.1.21.1.31.1.41.1.51.1.61.1.71.1.81.1.a11.1b11.21.2.11.2.21.2.31.2.41.2.51.2.61.2.72.02.0.12.0.102.0.112.0.122.0.132.0.14 |
5.2.46.0.1 |
History
| Recorded | Changed | Sources |
|---|---|---|
| first indexed | CVE List, EUVD, GitHub Advisories, NVD, OSV |
Dates are when Every CVE recorded each change. Upstream dates may differ.
In short
CVE-2026-55247 is a critical vulnerability (CVSS 9.1) in Plone Plone.app.event, published August 28, 2026. No source lists public exploit code. EPSS puts the chance of exploitation in the next 30 days at 0.44%, the 38th percentile. Fixed in plone-app-event 5.2.4.
References
github.com/plone/plone.app.event/security/advisories/GHSA-r82h-mqw3-fc56
Left out here: 152 versions. The JSON record has them.