What’s Vulnerable › Vulnerabilities

CVE-2023-45150: Inviting excessive long email addresses to a calendar event makes the Nextcloud server unresponsive

• Severity: medium (CVSS 4.3 v3.1)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 0.5% probability of exploitation in the next 30 days
• Public exploit or detection template: yes
• Published: 2023-10-16 · updated 2026-06-17
• Weakness: CWE-400

Description

Nextcloud calendar is a calendar app for the Nextcloud server platform. Due to missing precondition checks the server was trying to validate strings of any length as email addresses even when megabytes of data were provided, eventually making the server busy and unresponsive. It is recommended that the Nextcloud Calendar app is upgraded to 4.4.4. The only workaround for users unable to upgrade is to disable the calendar app.

Affected products

• Nextcloud Calendar application: from 1.0 before 4.4.4 — fixed in 4.4.4

How to fix

Upgrade to a fixed version: Nextcloud Calendar application 4.4.4. Check the vendor advisory for mitigations.

References

• https://github.com/nextcloud/calendar/pull/5358
• https://github.com/nextcloud/security-advisories/security/advisories/GHSA-r936-8gwm-w452
• https://hackerone.com/reports/2058337
• https://github.com/nextcloud/calendar/pull/5358
• https://github.com/nextcloud/security-advisories/security/advisories/GHSA-r936-8gwm-w452
• https://hackerone.com/reports/2058337

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