Vulnerability-Lookup

CVE-2026-55247 (GCVE-0-2026-55247)

Vulnerability from cvelistv5 – Published: 2026-08-28 18:59 – Updated: 2026-08-31 18:48

Title

plone.app.event: Denial of service via iCalendar import

Summary

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.

Severity

9.1 (Critical)


                        
                          CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:L/I:L/A:H

SSVC

Exploitation: none Automatable: no Technical Impact: partial

CISA Coordinator · CISA-ADP (v2.0.3)

Decision recorded 2026-08-31 18:48 UTC

CWE

CWE-400 - Uncontrolled Resource Consumption

Assigner

GitHub_M mitre root

References

5 references

URL	Tags
https://github.com/plone/plone.app.event/security…	x_refsource_CONFIRM
https://github.com/plone/plone.app.event/commit/1…	x_refsource_MISC
https://github.com/plone/plone.app.event/commit/4…	x_refsource_MISC
https://github.com/plone/plone.app.event/releases…	x_refsource_MISC
https://github.com/plone/plone.app.event/releases…	x_refsource_MISC

Impacted products

1 product

Vendor	Product	Version	CPE status
plone	plone.app.event	Affected: < 5.2.4 Affected: >= 6.0.0, < 6.0.1	guessed

Show details on NVD website

JSON

To clipboard

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FKIE_CVE-2026-55247

Vulnerability from fkie_nvd - Published: 2026-08-28 20:18 - Updated: 2026-08-31 19:16

Severity

9.1 (Critical) - CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:L/I:L/A:H

Summary

References

	URL	Tags
	security-advisories@github.com	https://github.com/plone/plone.app.event/commit/1e3c83c15a24d1a789cdb012593505bc5620e28e
	security-advisories@github.com	https://github.com/plone/plone.app.event/commit/4de5eb3ea9e4f7f1781622e6d64fc086629d1437
	security-advisories@github.com	https://github.com/plone/plone.app.event/releases/tag/5.2.4
	security-advisories@github.com	https://github.com/plone/plone.app.event/releases/tag/6.0.1
	security-advisories@github.com	https://github.com/plone/plone.app.event/security/advisories/GHSA-r82h-mqw3-fc56

Impacted products

	Vendor	Product	Version

JSON

To clipboard

{
  "affected": [
    {
      "affectedData": [
        {
          "product": "plone.app.event",
          "vendor": "plone",
          "versions": [
            {
              "status": "affected",
              "version": "\u003c 5.2.4"
            },
            {
              "status": "affected",
              "version": "\u003e= 6.0.0, \u003c 6.0.1"
            }
          ]
        }
      ],
      "source": "security-advisories@github.com"
    }
  ],
  "cveTags": [],
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    {
      "lang": "en",
      "value": "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\u0027s 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."
    }
  ],
  "id": "CVE-2026-55247",
  "lastModified": "2026-08-31T19:16:55.260",
  "metrics": {
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          "confidentialityImpact": "LOW",
          "integrityImpact": "LOW",
          "privilegesRequired": "LOW",
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GHSA-R82H-MQW3-FC56

Vulnerability from github – Published: 2026-08-28 18:59 – Updated: 2026-08-28 18:59

Summary

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

Details

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. Thank you!

Severity

9.1 (Critical)


                  
                    CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:L/I:L/A:H

Show details on source website

JSON

To clipboard

{
  "affected": [
    {
      "package": {
        "ecosystem": "PyPI",
        "name": "plone.app.event"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0"
            },
            {
              "fixed": "5.2.4"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    },
    {
      "package": {
        "ecosystem": "PyPI",
        "name": "plone.app.event"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "6.0.0a1"
            },
            {
              "fixed": "6.0.1"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    }
  ],
  "aliases": [
    "CVE-2026-55247"
  ],
  "database_specific": {
    "cwe_ids": [
      "CWE-400"
    ],
    "github_reviewed": true,
    "github_reviewed_at": "2026-08-28T18:59:42Z",
    "nvd_published_at": null,
    "severity": "CRITICAL"
  },
  "details": "### Impact\nBy 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.\n\n### Patches\nThe problem has been patched in `plone.app.event`.\n\n* For Plone 6.2: upgrade to `plone.app.event` 6.0.1\n* For Plone 6.1: upgrade to `plone.app.event` 5.2.4\n* For Plone 6.0: upgrade to `plone.app.event` 5.2.4\n\n### Workarounds\nIn 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.\n\nThere is no workaround for the stored XSS in the URL field of events.\n\nThe vulnerabilities were discovered by Timothy Dudley and responsibly reported to the [Plone Security Team](mailto:security@plone.org). Thank you!",
  "id": "GHSA-r82h-mqw3-fc56",
  "modified": "2026-08-28T18:59:42Z",
  "published": "2026-08-28T18:59:42Z",
  "references": [
    {
      "type": "WEB",
      "url": "https://github.com/plone/plone.app.event/security/advisories/GHSA-r82h-mqw3-fc56"
    },
    {
      "type": "WEB",
      "url": "https://github.com/plone/plone.app.event/commit/1e3c83c15a24d1a789cdb012593505bc5620e28e"
    },
    {
      "type": "WEB",
      "url": "https://github.com/plone/plone.app.event/commit/4de5eb3ea9e4f7f1781622e6d64fc086629d1437"
    },
    {
      "type": "PACKAGE",
      "url": "https://github.com/plone/plone.app.event"
    },
    {
      "type": "WEB",
      "url": "https://github.com/plone/plone.app.event/releases/tag/5.2.4"
    },
    {
      "type": "WEB",
      "url": "https://github.com/plone/plone.app.event/releases/tag/6.0.1"
    }
  ],
  "schema_version": "1.4.0",
  "severity": [
    {
      "score": "CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:L/I:L/A:H",
      "type": "CVSS_V3"
    }
  ],
  "summary": "plone.app.event vulnerable to denial of service via iCalendar import"
}

Sightings

Author	Source	Type	Date	Other

Nomenclature

Seen: The vulnerability was mentioned, discussed, or observed by the user.
Confirmed: The vulnerability has been validated from an analyst's perspective.
Published Proof of Concept: A public proof of concept is available for this vulnerability.
Exploited: The vulnerability was observed as exploited by the user who reported the sighting.
Patched: The vulnerability was observed as successfully patched by the user who reported the sighting.
Not exploited: The vulnerability was not observed as exploited by the user who reported the sighting.
Not confirmed: The user expressed doubt about the validity of the vulnerability.
Not patched: The vulnerability was not observed as successfully patched by the user who reported the sighting.

Detection rules are retrieved from Rulezet.

The MITRE ATT&CK techniques below are AI-generated suggestions, inferred from the description of the vulnerability by the CIRCL/vulnerability-attack-technique-classification-roberta-base model, served locally by ML-Gateway. They have not been verified by an analyst and are provided for guidance only.
The approach is described in our paper Mapping CVEs to MITRE ATT&CK Techniques: A Curated Gold-Set Classifier and the Limits of LLM-Assisted Label Expansion.

Action not permitted

CVE-2026-55247 (GCVE-0-2026-55247)

FKIE_CVE-2026-55247

GHSA-R82H-MQW3-FC56

Impact

Patches

Workarounds

Tags

Sightings

Nomenclature