Nextcloud ServerApplication · Nextcloud
CVE-2020-8139
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 · uneditedA missing access control check in Nextcloud Server < 18.0.1, < 17.0.4, and < 16.0.9 causes hide-download shares to be downloadable when appending /download to the URL.
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 fails to enforce the 'hide-download' flag on shares when the /download endpoint is accessed directly. By appending /download to a share URL, attackers can bypass the intended restriction and download files from shares that were configured to prevent downloads.
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
>= 16.0.0, < 16.0.9>= 17.0.0, < 17.0.4>= 18.0.0, < 18.0.1
FedoraOperating system
= 32CVSS 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
- None
- Availability
- None
CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/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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Check installed Nextcloud Server versionAccess the Nextcloud admin dashboard and navigate to Settings > Administration > Overview, or check the version file in the Nextcloud installation directory (version.php). Compare the version number to the affected ranges: 16.0.0 to <16.0.9, 17.0.0 to <17.0.4, or 18.0.0 to <18.0.1.Affected if The installed version falls within one of the affected version ranges.
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Identify shares with hide-download flag enabledIn Nextcloud, go to the Files app, locate shared items, and check share settings. The 'hide-download' option is typically found in the share settings dialog under 'Link share' options. Look for shares where download prevention is configured.Affected if There are shares configured with the hide-download flag enabled.
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Verify download endpoint accessibilityTake any share link (preferably one with hide-download enabled), append /download to the end of the URL, and attempt to access it in a browser or via curl. For example: https://your-nextcloud.example.com/s/ABC123/downloadAffected if The file downloads successfully despite the hide-download flag being set on that share.
The environment is affected if the installed Nextcloud Server version is 16.0.0-16.0.9, 17.0.0-17.0.4, or 18.0.0-18.0.1 AND there are shares with the hide-download flag enabled that can be bypassed via the /download endpoint.
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 data16.0.917.0.418.0.1
Upgrade to Nextcloud Server 18.0.1, 17.0.4, or 16.0.9 or later which includes the missing access control check for download endpoints.
Fix this in Nextcloud Server
Scoped from the published advisory
- Consultation2.0 h
- Implementation4.0 h
- Testing3.0 h
- Review / QA2.0 h
An estimate, not a bill — we confirm scope with you before any work starts. Need it this week? Rush from $3,088.
Scan for this in your stack
Free · runs locallyCheck whether your project pulls in CVE-2020-8139 — 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-2020-8139 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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- Verified mitigations, workarounds, and config changes
- Version or environment caveats, and links to real fixes
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