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Nextcloud ServerApplication · Nextcloud

CVE-2021-32679

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 →
95/100
Remediation priority · Urgent
Remotely reachable No privileges 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. In versions prior to 19.0.13, 20.0.11, and 21.0.3, filenames where not escaped by default in controllers using `DownloadResponse`. When a user-supplied filename was passed unsanitized into a `DownloadResponse`, this could be used to trick users into downloading malicious files with a benign file extension. This would show in UI behaviours where Nextcloud applications would display a benign file extension (e.g. JPEG), but the file will actually be downloaded with an executable file extension. The vulnerability is patched in versions 19.0.13, 20.0.11, and 21.0.3. Administrators of Nextcloud instances do not have a workaround available, but developers of Nextcloud apps may manually escape the file name before passing it into `DownloadResponse`.

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

A detailed technical summary for this CVE is being prepared.

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

CVSS:3.1/AV:N/AC:L/PR:N/UI:R/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

Nextcloud Server 19.0.13 (if upgrading from 18.x), 20.0.11 (if upgrading from 20.0.x), or 21.0.3 (if upgrading from 21.0.x)

  1. 1. Identify the currently running Nextcloud Server version in your environment
  2. 2. Based on your current version, determine the appropriate upgrade target: if on 18.x upgrade to 19.0.13; if on 20.x upgrade to 20.0.11; if on 21.x upgrade to 21.0.3
  3. 3. Back up the Nextcloud database and data directory before proceeding
  4. 4. Update the Nextcloud installation using the distribution's package manager or by downloading the official tarball from nextcloud.com
  5. 5. Run theocc upgrade command (if using the tarball method) to complete the database migration
  6. 6. Verify the upgrade was successful by logging into the web interface
  7. 7. Test that file downloads display the correct file extension to confirm the vulnerability is patched
Caveat Review Nextcloud's changelog for your target version for any breaking 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-2021-32679 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
  • No weaponised exploit code, or anything meant to cause harm
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