CVE-2023-48239: Nextcloud Server users can make external storage mount points inaccessible for other users

Severity: high (CVSS 7.1 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.9% probability of exploitation in the next 30 days
Public exploit or detection template: yes
Published: 2023-11-21 · updated 2026-06-17
Weakness: CWE-284

Description

Nextcloud Server provides data storage for Nextcloud, an open source cloud platform. Starting in version 25.0.0 and prior to versions 25.0.13, 26.0.8, and 27.1.3 of Nextcloud Server and starting in version 20.0.0 and prior to versions 20.0.14.16, 21.0.9.13, 22.2.10.15, 23.0.12.12, 24.0.12.8, 25.0.13, 26.0.8, and 27.1.3 of Nextcloud Enterprise Server, a malicious user could update any personal or global external storage, making them inaccessible for everyone else as well. Nextcloud Server 25.0.13, 26.0.8, and 27.1.3 and Nextcloud Enterprise Server is upgraded to 20.0.14.16, 21.0.9.13, 22.2.10.15, 23.0.12.12, 24.0.12.8, 25.0.13, 26.0.8, and 27.1.3 contain a patch for this issue. As a workaround, disable app files_external. This workaround also makes the external storage inaccessible but retains the configurations until a patched version has been deployed.

Affected products

Nextcloud Server: from 20.0.0 before 20.0.14.16; from 21.0.0 before 21.0.9.13; from 22.0.0 before 22.2.10.15; from 23.0.0 before 23.0.12.12; from 24.0.0 before 24.0.12.8; from 25.0.0 before 25.0.13 — fixed in 20.0.14.16, 21.0.9.13, 22.2.10.15, 23.0.12.12, 24.0.12.8, 25.0.13

How to fix

Upgrade to a fixed version: Nextcloud Server 20.0.14.16, 21.0.9.13, 22.2.10.15, 23.0.12.12. Check the vendor advisory for mitigations.

References

Get alerted when CVE-2023-48239 or the next vulnerability affects your stack