CVE-2026-55247Network attack vector

Site disruption and SSRF via unbounded iCalendar import

Published Aug 28, 2026 · Updated Aug 28, 2026

iCalendar import flaws in Plone plone.app.event before 5.2.4 and 6.0.0 allow remote authenticated users to disrupt sites. The importer accepts insufficiently restricted calendar URLs, downloads and imports without adequate byte or event limits, commits each event, and stores event URLs without blocking script schemes. Editor access is required; exploitation can force internal or local-file requests, exhaust server resources until the site goes offline, or execute stored script in another user's browser.

CVSS severity9.1
Critical
EPSS probability0.34%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

iCalendar import flaws in Plone plone.app.event before 5.2.4 and 6.0.0 allow remote authenticated users to disrupt sites. The importer accepts insufficiently restricted calendar URLs, downloads and imports without adequate byte or event limits, commits each event, and stores event URLs without blocking script schemes. Editor access is required; exploitation can force internal or local-file requests, exhaust server resources until the site goes offline, or execute stored script in another user's browser.

The record

CVE
CVE-2026-55247
Published
Aug 28, 2026
Updated
Aug 28, 2026
Vendor
Plone
Product
plone.app.event
Classifications
CWE-400, T1499.003
Attack vector
network
Privileges
authenticated

Timeline

How it unfolded

  1. Aug 28, 2026CVE publishedPublication date reported by the CVE source.
  2. Aug 28, 2026Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=< 5.2.4
  2. Affected versionversion=>= 6.0.0, < 6.0.1

What conditions does exploitation require?

Attack vectornetwork
Required privilegesauthenticated

What is affected?

Plone · plone.app.eventversion=< 5.2.4; version=>= 6.0.0, < 6.0.1

Published CVSS scores

9.1GitHubCVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:L/I:L/A:H

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-400Uncontrolled Resource Consumption
T1499.003Application Exhaustion Flood

Public exploit references

No public exploit references are available in this record.

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Technologies

Your stack

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Your stack

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