Nextcloud Calendar app allowed booking appointments without the generated token
Priority LOW 15CWE-639Published · Updated
Key facts
- Attack vector
- Local
- Privileges required
- Low
- User interaction
- None
- Attack complexity
- Low
- Impact type
- Security bypass
- Confidentiality · integrity · availability
- Low · None · None
- Fix status
- Fixed
Attack profile from CVSS 3.1 · CNA. Fix status from CNA. Impact type from CWE-639.
Summary
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.
Why it matters now
Exploitation None reported CISA SSVC · not in CISA KEV
EPSS 0.00149 4th percentileScored 2026-11-07
Fix Fixed security-advisories (nextcloud): 6.0.1, 5.5.6, 4.7.19
SSVC decision points
CISA ADP · SSVC 2.0.3
- Exploitation
- None
- Automatable
- No
- Technical impact
- Partial
The decision (Track, Attend, Act) also depends on your mission and well-being impact; see CISA's SSVC guide.
Affected products
| Vendor | Product | Affected versions | Fixed in | Status | Source |
|---|---|---|---|---|---|
| nextcloud | security-advisories | 6.0.0-rc.1 to before 6.0.1; 5.0.0-rc.1 to before 5.5.6; 3.0.0-beta1 to before 4.7.19 | 6.0.1, 5.5.6, 4.7.19 | Patch available | CNA |
- security-advisories Vendornextcloud Affected 6.0.0-rc.1 to before 6.0.1; 5.0.0-rc.1 to before 5.5.6; 3.0.0-beta1 to before 4.7.19 Fixed in 6.0.1, 5.5.6, 4.7.19 Patch available CNA
CPE configurations NVD · 8
| CPE | Versions | Role | Vendor |
|---|---|---|---|
| cpe:2.3:a:nextcloud:calendar:*:*:*:*:*:*:*:* | 4.0.0 to before 4.7.19; 5.0.0 to before 5.5.6 | Vulnerable | nextcloud |
| cpe:2.3:a:nextcloud:calendar:6.0.0:-:*:*:*:*:*:* | 6.0.0 | Vulnerable | nextcloud |
| cpe:2.3:a:nextcloud:calendar:6.0.0:rc1:*:*:*:*:*:* | 6.0.0 rc1 | Vulnerable | nextcloud |
| cpe:2.3:a:nextcloud:calendar:6.0.0:rc2:*:*:*:*:*:* | 6.0.0 rc2 | Vulnerable | nextcloud |
| cpe:2.3:a:nextcloud:calendar:6.0.0:rc3:*:*:*:*:*:* | 6.0.0 rc3 | Vulnerable | nextcloud |
| cpe:2.3:a:nextcloud:calendar:6.0.0:rc4:*:*:*:*:*:* | 6.0.0 rc4 | Vulnerable | nextcloud |
| cpe:2.3:a:nextcloud:calendar:6.0.0:rc5:*:*:*:*:*:* | 6.0.0 rc5 | Vulnerable | nextcloud |
| cpe:2.3:a:nextcloud:calendar:6.0.0:rc6:*:*:*:*:*:* | 6.0.0 rc6 | Vulnerable | nextcloud |
- cpe:2.3:a:nextcloud:calendar:*:*:*:*:*:*:*:* Versions 4.0.0 to before 4.7.19; 5.0.0 to before 5.5.6 Vulnerable ·nextcloud
- cpe:2.3:a:nextcloud:calendar:6.0.0:-:*:*:*:*:*:* Versions 6.0.0 Vulnerable ·nextcloud
- cpe:2.3:a:nextcloud:calendar:6.0.0:rc1:*:*:*:*:*:* Versions 6.0.0 rc1 Vulnerable ·nextcloud
- cpe:2.3:a:nextcloud:calendar:6.0.0:rc2:*:*:*:*:*:* Versions 6.0.0 rc2 Vulnerable ·nextcloud
- cpe:2.3:a:nextcloud:calendar:6.0.0:rc3:*:*:*:*:*:* Versions 6.0.0 rc3 Vulnerable ·nextcloud
- cpe:2.3:a:nextcloud:calendar:6.0.0:rc4:*:*:*:*:*:* Versions 6.0.0 rc4 Vulnerable ·nextcloud
- cpe:2.3:a:nextcloud:calendar:6.0.0:rc5:*:*:*:*:*:* Versions 6.0.0 rc5 Vulnerable ·nextcloud
- cpe:2.3:a:nextcloud:calendar:6.0.0:rc6:*:*:*:*:*:* Versions 6.0.0 rc6 Vulnerable ·nextcloud
Remediation
- Fix · CNA security-advisories (nextcloud) Fixed in 6.0.1, 5.5.6, 4.7.19
Timeline
- 2026-10-02 Threatist record created from CVE-2025-66546
References
More nextcloud Calendar vulnerabilities
- TI-2022-08650 Command Injection in Appointment Emails for Nextcloud Calendar CVSS 3.1CRITICAL 9.8
- TI-2023-24171 Inviting excessive long email addresses to a calendar event makes the Nextcloud server unresponsive CVSS 3.1MEDIUM 4.3
- TI-2023-26171 Calendar app returns full stacktrace when an error happens while editing appointment CVSS 3.1MEDIUM 6.5
- TI-2025-40933 Nextcloud Calendar app used predictable proposal participant tokens CVSS 3.1MEDIUM 6.5
- TI-2025-40961 Nextcloud Calendar attachments of local files are offered to downloaded CVSS 3.1MEDIUM 5.7
- TI-2018-02759 Cross-site scripting in Nextcloud Calendar application CVSS 3.1MEDIUM 4.8
Sources
This product uses the NVD API but is not endorsed or certified by the NVD. Sources and licences