Nextcloud ServerApplication · Nextcloud
CVE-2021-32656
Official description Straight from the sourceThe vendor's or NVD's own wording, published unedited. Authoritative, but often terse — it says what broke, rarely what to do.
NVD · uneditedNextcloud 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.
Technical summary Written by usOur analysis, written from the advisory, the CVSS vector and the affected-version data. It adds context the advisory leaves out, and never invents facts that are not in the source.
dbcve analysis · high confidenceNextcloud Server versions prior to 19.0.11, 20.0.10, and 21.0.2 contain an information disclosure vulnerability in the federated share functionality. When users add public links as federated shares with the automatic server addition setting enabled, attackers can exploit this to access basic user information (usernames, email addresses) from the target Nextcloud server without authentication.
Verify against the referenced sources before acting — the references below are authoritative for this CVE, this summary is not.
Affected products & versions What the vendor confirmedThe version ranges the vendor confirmed as vulnerable. If your version sits inside a range here, treat yourself as exposed until you have upgraded.
NVD · CPE data
Nextcloud ServerApplication
< 19.0.11>= 20.0.0, < 20.0.10>= 21.0.0, < 21.0.2CVSS breakdown How the score is builtThe industry scoring standard. It rates how the flaw is reached, what it takes to exploit, and what an attacker gains — the score is derived from those, not the other way round.
From the vector- Attack vector
- Network
- Complexity
- Low
- Privileges
- None
- User interaction
- None
- Scope
- Changed
- Confidentiality
- High
- Integrity
- None
- Availability
- None
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:N/A:N
Am I affected? How to checkSteps we derive from the advisory and the affected-version data, so you can decide whether this CVE reaches your setup. They are a guide, not a scan — your own configuration is the authority.
dbcve checksWork through these to decide whether this CVE applies to you.
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Determine installed Nextcloud Server versionRun 'occ --version' from the Nextcloud installation directory, or view the version in the web interface under Administration > Overview, or check the 'version' entry in config/config.phpAffected if Version is below 19.0.11, OR between 20.0.0 and 20.0.10 inclusive, OR between 21.0.0 and 21.0.2 inclusive
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Verify federated sharing is enabledCheck the Nextcloud admin panel under Administration > Sharing > Federated Cloud Sharing, or run 'occ config:app:get core shareapi_remote_wipe' and check for federation app enabled statusAffected if Federated sharing is enabled (this is required for the vulnerability to be exploitable)
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Check the automatic server addition settingRun 'occ config:app:get federation autoAddServers' or inspect the database table 'oc_appconfig' for the key 'autoAddServers' in the 'federation' app, or view the checkbox 'Add server automatically once a federated share was created successfully' in Administration > Sharing settingsAffected if The 'autoAddServers' setting value is 'yes' or 'true' (this specific setting must be enabled for the flaw to apply)
You are affected if your Nextcloud Server version falls within the vulnerable ranges AND the automatic server addition setting for federated shares is enabled.
Generated from the published advisory. Verify against your own configuration.
Remediation Closing itWhat it takes to close this. Where a vendor fix exists we point at it; where none exists we say so plainly, and can build one. Effort estimates are scoped from the advisory, not from your codebase.
From vendor data19.0.1120.0.1021.0.2
Upgrade to Nextcloud Server versions 19.0.11, 20.0.10, or 21.0.2 or later. Alternatively, disable the 'Add server automatically once a federated share was created successfully' setting in the Nextcloud administrative settings to block automatic federated server trust.
Fix this in Nextcloud Server
Scoped from the published advisory
- Consultation2.0 h
- Implementation3.0 h
- Testing2.0 h
- Review / QA1.0 h
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Scan for this in your stack
Free · runs locallyCheck whether your project pulls in CVE-2021-32656 — or any other known-vulnerable package — straight from your lock files. Free and open source; it runs locally and uploads nothing.
References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.
Primary sourcesPractitioner notes
ContributedPeer-ranked notes from engineers who’ve handled CVE-2021-32656 in production — separate from our analysis above.
The advisory tells you what broke. It rarely tells you what actually worked. If you’ve dealt with this one, that detail is what the next engineer is searching for.
- The version that genuinely resolved it — not the one the vendor claimed
- A config change or rule that shut the vector down
- A gotcha in the upgrade path that cost you an afternoon
No notes yet
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- Version or environment caveats, and links to real fixes
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