Attacker can obtain write access to any federated share/public link

Description

Impact

An attacker is able to receive write/read privileges on any Federated File Share. Since public links can be added as federated file share, this can also be exploited on any public link. (e.g. to add malicious data into a folder, or get read access to a “Files Drop” link).

Patches

It is recommended that the Nextcloud Server is upgraded to 19.0.11, 20.0.10 or 21.0.2.

Workarounds

Disable Federated File Sharing.

References

• HackerOne

For more information

If you have any questions or comments about this advisory:

• Create a post in nextcloud/security-advisories
• Customers: Open a support ticket at support.nextcloud.com