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CVE-2023-39952 - Nextcloud Server
Nextcloud Server provides data storage for Nextcloud, an open source cloud platform. Starting in version 22.0.0 and prior to versions 22.2.10.13, 23.0.12.8, 24.0.12.4, 25.0.8, 26.0.3, and 27.0.1, a user can access files inside a subfolder of a groupfolder accessible to them, even if advanced permissions would block access to the subfolder. Nextcloud Server versions 25.0.8, 26.0.3, and 27.0.1 and Nextcloud Enterprise Server versions 22.2.10.13, 23.0.12.8, 24.0.12.4, 25.0.8, 26.0.3, and 27.0.1 contain a patch for this issue. No known workarounds are available.
References
https://github.com/nextcloud/groupfolders/issues/1906
https://github.com/nextcloud/security-advisories/security/advisories/GHSA-cq8w-v4fh-4rjq
https://github.com/nextcloud/server/pull/38890
https://hackerone.com/reports/1808079