Nextcloud calendar vulnerabilities

Latest Nextcloud calendar CVEs

Newest publication first

1. CVE-2026-45286 Nextcloud: Calendar app leaked user identifiers via attendee suggestion endpoint

   Published 2026-06-01

   Medium·CVSS 4.3 EPSS 0.28%

   Nextcloud is an open source content collaboration platform. From versions 5.5.13 to before 5.5.17, and 6.2.0 to before 6.2.3, an authenticated user can enumerate users on the same Nextcloud instance by using the Calendar app's endpoint for suggesting attendees. The sharing restri...

2. CVE-2025-66550 Nextcloud Calendar attachments of local files are offered to downloaded

   Published 2025-12-05

   Medium·CVSS 5.7 EPSS 0.37%

   Nextcloud Calendar is a calendar app for Nextcloud. Prior to 4.7.17 and 5.2.4, when a malicious user creates a calendar event with a crafted attachment that links to a download link of a file on the same Nextcloud server, the file would be downloaded without the user confirming t...

3. CVE-2025-66546 Nextcloud Calendar app allowed booking appointments without the generated token

   Published 2025-12-05

   Low·CVSS 3.3 EPSS 0.15%

   Nextcloud Calendar is a calendar app for Nextcloud. Prior to 4.7.19, 5.5.6, and 6.0.1, the calendar app allowed blindly booking appointments with a squential ID without known the appointment token. This vulnerability is fixed in 4.7.19, 5.5.6, and 6.0.1.

4. CVE-2025-66511 Nextcloud Calendar app used predictable proposal participant tokens

   Published 2025-12-05

   Medium·CVSS 6.5 EPSS 0.32%

   Nextcloud Calendar is a calendar app for Nextcloud. Prior to 6.0.3, the Calendar app generates participant tokens for meeting proposals using a hash function, allowing an attacker to compute valid participant tokens, which allowed them to request details and submit dates in meeti...

5. CVE-2024-37316 Nextcloud Calendar's event create can create attachments that link to other websites

   Published 2024-06-14

   Medium·CVSS 4.6 EPSS 0.36%

   Nextcloud Calendar is a calendar app for Nextcloud. Authenticated users could create an event with manipulated attachment data leading to a bad redirect for participants when clicked. It is recommended that the Nextcloud Calendar App is upgraded to 4.6.8 or 4.7.2.

6. CVE-2023-48308 Calendar app returns full stacktrace when an error happens while editing appointment

   Published 2023-12-21

   Medium·CVSS 6.5 EPSS 0.55%

   Nextcloud/Cloud is a calendar app for Nextcloud. An attacker can gain access to stacktrace and internal paths of the server when generating an exception while editing a calendar appointment. It is recommended that the Nextcloud Calendar app is upgraded to 4.5.3

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

   Published 2023-10-16

   Medium·CVSS 4.3 EPSS 0.48%

   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...

8. CVE-2023-33183 Error in calendar when booking an appointment reveals the full path of the website

   Published 2023-05-30

   Medium·CVSS 4.3 EPSS 0.44%

   Calendar app for Nextcloud easily sync events from various devices with your Nextcloud. Some internal paths of the website are disclosed when the SMTP server is unavailable. It is recommended that the Calendar app is updated to 3.5.5 or 4.2.3

9. CVE-2022-24838 Command Injection in Appointment Emails for Nextcloud Calendar

   Published 2022-04-11

   Critical·CVSS 9.8 EPSS 33.0%

   Nextcloud Calendar is a calendar application for the nextcloud framework. SMTP Command Injection in Appointment Emails via Newlines: as newlines and special characters are not sanitized in the email value in the JSON request, a malicious attacker can inject newlines to break out...

10. CVE-2018-3763 In Nextcloud Calendar before 1.5.8 and 1.6.1, a missing sanitization of search results for an autocomplete field could lead to a stored XSS requiring user-interaction. The missing sanitization only af...

    Published 2018-07-05

    Medium·CVSS 4.8 EPSS 0.61%

    In Nextcloud Calendar before 1.5.8 and 1.6.1, a missing sanitization of search results for an autocomplete field could lead to a stored XSS requiring user-interaction. The missing sanitization only affected group names, hence malicious search results could only be crafted by priv...

Sources: CVE.org, NVD, CISA KEV, FIRST EPSS, OSV and public exploit-reference metadata. Product matching comes from the published CVE records. A proof-of-concept means public code exists; it is not evidence of exploitation.