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Nextcloud ServerApplication · Nextcloud

CVE-2021-32802

CRITICAL · 9.8 CVSS v3.1 Published 2021-09-07
Fix available
A fix is available. Upgrade to 20.0.12 / 21.0.4 or later.
See remediation →
100/100
Remediation priority · Urgent
Remotely reachable No privileges Zero-click

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 an open source, self hosted personal cloud. Nextcloud supports rendering image previews for user provided file content. For some image types, the Nextcloud server was invoking a third-party library that wasn't suited for untrusted user-supplied content. There are several security concerns with passing user-generated content to this library, such as Server-Side-Request-Forgery, file disclosure or potentially executing code on the system. The risk depends on your system configuration and the installed library version. It is recommended that the Nextcloud Server is upgraded to 20.0.12, 21.0.4 or 22.1.0. These versions do not use this library anymore. As a workaround users may disable previews by setting `enable_previews` to `false` in `config.php`.

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 confidence

Nextcloud Server used a third-party image processing library unsuitable for untrusted user content when rendering image previews. This allowed potential Server-Side Request Forgery, file disclosure, or remote code execution depending on system configuration and library version. The fixed versions (20.0.12, 21.0.4, 22.1.0) removed this unsafe library dependency.

MitigationUpgrade Nextcloud Server to version 20.0.12, 21.0.4, or 22.1.0 (or later). Alternatively, disable image previews by setting `enable_previews` to `false` in config.php as a workaround.

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
Affected:< 20.0.12>= 21.0.0, < 21.0.4>= 22.0.0, < 22.1.0

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

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

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 checks

Work through these to decide whether this CVE applies to you.

  1. Determine installed Nextcloud version
    Locate the version.php file in the Nextcloud root directory (e.g., /var/www/nextcloud/version.php) or run `occ --version` from the Nextcloud directory
    Affected if The version number is less than 20.0.12, or falls between 21.0.0-21.0.3, or falls between 22.0.0-22.0.x
  2. Verify if image previews are enabled
    Check the Nextcloud config.php file (usually in config/config.php) for the setting `enable_previews`. If the setting is absent, previews are enabled by default.
    Affected if The `enable_previews` setting is set to true or is absent from config.php (defaults to true)
  3. Confirm preview functionality is in use
    Inspect the data directory for any preview images in the appdata_*/preview folder, or check if users have uploaded images that would generate previews
    Affected if Preview images exist in the data directory, indicating the preview system is active

You are affected if your Nextcloud Server version is within the vulnerable range AND image previews are enabled (the default setting), as the exploit targets the image preview rendering component.

Generated from the published advisory. Verify against your own configuration.

Check your environment

Paste your version and any relevant configuration and it will be compared against the affected criteria above. Do not include secrets or credentials.

AI-assisted, checked against the advisory. Informational, not a guarantee.

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 20.0.12 / 21.0.4 / 22.1.0 or later
Fixed in 20.0.1221.0.422.1.0
Interim mitigation

Upgrade Nextcloud Server to version 20.0.12, 21.0.4, or 22.1.0 (or later). Alternatively, disable image previews by setting `enable_previews` to `false` in config.php as a workaround.

Recommended fix High confidence

Upgrade to 20.0.12, 21.0.4, or 22.1.0 (or later stable release)

  1. Upgrade Nextcloud Server to version 20.0.12, 21.0.4, or 22.1.0 (or later stable release)
  2. After upgrade, verify that image previews function correctly with the new preview rendering implementation
  3. Alternatively, as a temporary workaround, edit config.php and set 'enable_previews' => false to disable the vulnerable preview functionality
Caveat Disabling previews will remove the image thumbnail/preview functionality for users

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

Fix this in Nextcloud Server Scoped from the published advisory
  • Consultation2.0 h
  • Implementation4.0 h
  • Testing3.0 h
  • Review / QA1.0 h
10.0 hours of engineering $1,750
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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-2021-32802 in production — separate from our analysis above.

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What this is

A place for practitioners to share what actually worked: a mitigation you’ve tested, a configuration change, a version- or environment-specific caveat, or a link to a verified patch. The most useful notes rise to the top as peers upvote them, so the signal stays high.

What belongs here
  • Verified mitigations, workarounds, and config changes
  • Version or environment caveats, and links to real fixes
  • No weaponised exploit code, or anything meant to cause harm
  • No spam, self-promotion, credentials, or personal data