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Nextcloud ServerApplication · Nextcloud

CVE-2021-32688

HIGH · 8.8 CVSS v3.1 Published 2021-07-12
Fix available
A fix is available. Upgrade to 19.0.13 / 20.0.11 or later.
See remediation →
94/100
Remediation priority · Urgent
Remotely reachable Zero-click Patch available

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 · unedited
Nextcloud Server is a Nextcloud package that handles data storage. Nextcloud Server supports application specific tokens for authentication purposes. These tokens are supposed to be granted to a specific applications (e.g. DAV sync clients), and can also be configured by the user to not have any filesystem access. Due to a lacking permission check, the tokens were able to change their own permissions in versions prior to 19.0.13, 20.0.11, and 21.0.3. Thus fileystem limited tokens were able to grant themselves access to the filesystem. The issue is patched in versions 19.0.13, 20.0.11, and 21.0.3. There are no known workarounds aside from upgrading.

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
How this class of weakness works · CWE-285

The application confirms who you are but does not properly check whether you are permitted to perform a given action, so authenticated users reach functions or data meant for others. Attackers test roles and object references to find the gap. Remediation is an authorization check on every request, evaluated against the acting user's actual permissions.

General guidance for the improper authorization class — the official description and references above are authoritative for this specific CVE. Want a bespoke review and a reviewed fix? Ask our team →

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
Affected:< 19.0.13>= 20.0.0, < 20.0.11>= 21.0.0, < 21.0.3
FedoraOperating system
Affected:= 33= 34

CVSS 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
Low
User interaction
None
Scope
Unchanged
Confidentiality
High
Integrity
High
Availability
High

CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H

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.

dbcve · scoped
Upgrade available Upgrade to 19.0.13 / 20.0.11 / 21.0.3 or later
Fixed in 19.0.1320.0.1121.0.3
Vendor patch github.com →
Recommended fix High confidence

Upgrade to Nextcloud Server 19.0.13 (if on v19.x), 20.0.11 (if on v20.x), or 21.0.3 (if on v21.x)

  1. 1. Identify your current Nextcloud Server version in the admin settings or by checking the version file
  2. 2. Create a complete backup of your Nextcloud data directory, database, and config.php file
  3. 3. For package-based installations (e.g., on Debian/Ubuntu with the official repository): Run 'apt update && apt install nextcloud-server' or your distribution's package manager to upgrade to the latest available version
  4. 4. For manual installations: Download the appropriate version from https://nextcloud.com/install/#instructions-server (19.0.13, 20.0.11, or 21.0.3)
  5. 5. Extract the new version over your existing installation directory, preserving your config.php and data directory
  6. 6. Run theocc maintenance:mode --on command to enable maintenance mode
  7. 7. Run theocc upgrade command to complete the database schema migration
  8. 8. Run theocc maintenance:mode --off to disable maintenance mode
Caveat Standard Nextcloud patch upgrades typically have minimal breaking changes, but always review the Nextcloud changelog for your version for any notable changes or deprecations before upgrading

Generated from the published advisory — verify against the referenced sources before acting.

We can perform the upgrade in your staging environment and verify nothing breaks — typical engagement from $1,950. Get the upgrade done

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References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.

Primary sources

Practitioner notes

Contributed

Peer-ranked notes from engineers who’ve handled CVE-2021-32688 in production — separate from our analysis above.

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What this is

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What belongs here
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  • Version or environment caveats, and links to real fixes
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