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Nextcloud ServerApplication · Nextcloud

CVE-2023-48239

HIGH · 7.1 CVSS v3.1 Published 2023-11-21
Fix available
A fix is available. Upgrade to 20.0.14.16 / 21.0.9.13 or later.
See remediation →
77/100
Remediation priority · High
Public exploit 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 provides data storage for Nextcloud, an open source cloud platform. Starting in version 25.0.0 and prior to versions 25.0.13, 26.0.8, and 27.1.3 of Nextcloud Server and starting in version 20.0.0 and prior to versions 20.0.14.16, 21.0.9.13, 22.2.10.15, 23.0.12.12, 24.0.12.8, 25.0.13, 26.0.8, and 27.1.3 of Nextcloud Enterprise Server, a malicious user could update any personal or global external storage, making them inaccessible for everyone else as well. Nextcloud Server 25.0.13, 26.0.8, and 27.1.3 and Nextcloud Enterprise Server is upgraded to 20.0.14.16, 21.0.9.13, 22.2.10.15, 23.0.12.12, 24.0.12.8, 25.0.13, 26.0.8, and 27.1.3 contain a patch for this issue. As a workaround, disable app files_external. This workaround also makes the external storage inaccessible but retains the configurations until a patched version has been deployed.

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-284

The application fails to correctly restrict what a user can do or reach, so functions or resources are available to people who should not have them. Attackers simply probe for the paths where the check is missing or wrong. The fix is to enforce access-control decisions consistently on every request, evaluated against the acting user rather than assumed from context.

General guidance for the improper access control 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:>= 20.0.0, < 20.0.14.16>= 21.0.0, < 21.0.9.13>= 22.0.0, < 22.2.10.15>= 23.0.0, < 23.0.12.12>= 24.0.0, < 24.0.12.8>= 25.0.0, < 25.0.13>= 26.0.0, < 26.0.8>= 27.0.0, < 27.1.3

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
None
Integrity
Low
Availability
High

CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:L/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 20.0.14.16 / 21.0.9.13 / 22.2.10.15 or later
Fixed in 20.0.14.1621.0.9.1322.2.10.15
Vendor patch github.com →
Recommended fix High confidence

20.0.14.16, 21.0.9.13, 22.2.10.15, or 23.0.12.12 (or respective later versions in each branch)

  1. Upgrade Nextcloud Server to version 20.0.14.16 or higher for the 20.x branch
  2. Alternatively, upgrade to version 21.0.9.13 or higher for the 21.x branch
  3. Alternatively, upgrade to version 22.2.10.15 or higher for the 22.x branch
  4. Alternatively, upgrade to version 23.0.12.12 or higher for the 23.x branch
  5. As a workaround if immediate upgrade is not possible, disable the 'files_external' app via the Nextcloud admin interface or occ command: occ app:disable files_external
Caveat Standard upgrade procedures apply; ensure backup of data and config before upgrading; test upgrade in staging environment first

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-2023-48239 in production — separate from our analysis above.

No notes yet

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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
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