CVE-2025-66511— Nextcloud Calendar app used predictable proposal participant tokens
Quick assessment
Affected
nextcloud security-advisories
Exploitation
No confirmed in-the-wild exploitation; assess based on exposure
Recommended action
Check the vendor advisory and references for a fixed version. If immediate upgrade is impossible, restrict exposure and increase monitoring.
Nextcloud Calendar是Nextcloud开源的一个日历应用程序。 Nextcloud Calendar 6.0.3之前版本存在安全特征问题漏洞，该漏洞源于会议提案参与者令牌生成方式不安全，可能导致令牌被计算。
Possible ATT&CK Techniques 1 AI
T1078 · Valid Accounts
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I. Basic Information for CVE-2025-66511
Vulnerability Information
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Vulnerability Title
Nextcloud Calendar app used predictable proposal participant tokens
Source: CVE Program / CVE List V5
Vulnerability Description
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 meeting proposals. The tokens are not purely random generated. This vulnerability is fixed in 6.0.3.
Source: CVE Program / CVE List V5
CVSS Information
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:L/A:N
Source: CVE Program / CVE List V5
Vulnerability Type
使用不充分的随机数
Source: CVE Program / CVE List V5
Vulnerability Title
Nextcloud Calendar 安全特征问题漏洞
Source: CNNVD (China National Vulnerability Database)
Vulnerability Description
Nextcloud Calendar是Nextcloud开源的一个日历应用程序。 Nextcloud Calendar 6.0.3之前版本存在安全特征问题漏洞，该漏洞源于会议提案参与者令牌生成方式不安全，可能导致令牌被计算。
Source: CNNVD (China National Vulnerability Database)
CVSS Information
N/A
Source: CNNVD (China National Vulnerability Database)
Vulnerability Type
N/A
Source: CNNVD (China National Vulnerability Database)
Affected Products
| Vendor | Product | Affected Versions | CPE | Subscribe |
|---|---|---|---|---|
| nextcloud | security-advisories | >= 6.0.0-rc.1, < 6.0.3 | - |
|
II. Public POCs for CVE-2025-66511
| # | POC Description | Source Link | Shenlong Link |
|---|
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Same Patch Batch · nextcloud · 2025-12-05 · 19 CVEs total
| CVE-2025-66551 | 6.3 MEDIUM | Nextcloud Tables is missing an ownership check which allows moving columns into tables of |
| CVE-2025-66550 | 5.7 MEDIUM | Nextcloud Calendar attachments of local files are offered to downloaded |
| CVE-2025-66512 | 5.4 MEDIUM | Nextcloud Server vulnerable to XSS in SVG images when opened outside of Nextcloud |
| CVE-2025-66557 | 5.4 MEDIUM | Nextcloud Deck app allowed user with "Can share" permission to modify permissions of other |
| CVE-2025-66510 | 4.5 MEDIUM | Nextcloud Server Contacts Search allowed users to retrieve contact information of other us |
| CVE-2025-66553 | 4.3 MEDIUM | Nextcloud Tables app allowed users to view columns metadata information of any table |
| CVE-2025-66547 | 4.3 MEDIUM | Nextcloud Server users can modify tags on files that do not belong to them |
| CVE-2025-66552 | 4.3 MEDIUM | Nextcloud Server admin_audit does not log all actions on files in groupfolders |
| CVE-2025-66513 | 4.3 MEDIUM | Nextcloud Tables app share information not limited to relevant users |
| CVE-2025-66514 | 3.5 LOW | Nextcloud Mail stored HTML injection in subject text |
| CVE-2025-66545 | 3.5 LOW | Nextcloud Groupfolders users with read-only permissions for team folder can restore delete |
| CVE-2025-66554 | 3.5 LOW | Nextcloud Contacts vulnerable to Stored XSS in contacts app via organisation and title fie |
| CVE-2025-66556 | 3.5 LOW | Nextcloud talk allows participants to blindly delete poll drafts of other users by ID |
| CVE-2025-66548 | 3.3 LOW | Nextcloud Deck app allows to spoof file extensions by using RTLO characters |
| CVE-2025-66546 | 3.3 LOW | Nextcloud Calendar app allowed booking appointments without the generated token |
| CVE-2025-66558 | 3.1 LOW | Nextcloud Twofactor WebAuthn app was updated based on public key |
| CVE-2025-66515 | 2.7 LOW | Nextcloud Approval app allows users to request approval for other users file |
| CVE-2025-66549 | 2.4 LOW | Nextcloud Desktop discloses information when attempting to lock a file inside a end-to-end |
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