CVE-2021-32656: Trusted servers exchange can be triggered by attacker

Severity: high (CVSS 8.6 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 1.8% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2021-06-01 · updated 2026-06-17
Weakness: CWE-284

Description

Nextcloud Server is a Nextcloud package that handles data storage. A vulnerability in federated share exists in versions prior to 19.0.11, 20.0.10, and 21.0.2. An attacker can gain access to basic information about users of a server by accessing a public link that a legitimate server user added as a federated share. This happens because Nextcloud supports sharing registered users with other Nextcloud servers, which can be done automatically when selecting the "Add server automatically once a federated share was created successfully" setting. The vulnerability is patched in versions 19.0.11, 20.0.10, and 21.0.2 As a workaround, disable "Add server automatically once a federated share was created successfully" in the Nextcloud settings.

Affected products

Nextcloud Server: before 19.0.11; from 20.0.0 before 20.0.10; from 21.0.0 before 21.0.2 — fixed in 19.0.11, 20.0.10, 21.0.2

How to fix

Upgrade to a fixed version: Nextcloud Server 19.0.11, 20.0.10, 21.0.2. Check the vendor advisory for mitigations.

References

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