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Nextcloud ServerApplication · Nextcloud

CVE-2020-8155

MEDIUM · 5.4 CVSS v3.1 Published 2020-05-12
Fix available
A fix is available. Upgrade to 18.0.3 or later.
See remediation →
58/100
Remediation priority · Elevated
Remotely reachable

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
An outdated 3rd party library in the Files PDF viewer for Nextcloud Server 18.0.2 caused a Cross-site scripting vulnerability when opening a malicious PDF.

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 · moderate confidence

A Cross-site scripting (XSS) vulnerability exists in the Files PDF viewer of Nextcloud Server 18.0.2 due to an outdated third-party library. An attacker can craft a malicious PDF file that, when opened by a victim through the PDF viewer, executes arbitrary JavaScript in the context of the user's session.

MitigationUpdate Nextcloud Server to a version that includes the patched PDF viewer library, or manually upgrade the underlying third-party PDF library to a version without the XSS vulnerability.

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:< 18.0.3

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
Required
Scope
Changed
Confidentiality
Low
Integrity
Low
Availability
None

CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:C/C:L/I:L/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 checks

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

  1. Check Nextcloud Server version
    Log into the Nextcloud administrative interface and navigate to the settings page to view the server version, or run the command 'occ --version' from the Nextcloud directory if you have CLI access
    Affected if The displayed version is any version before 18.0.3 (for example, 18.0.0, 18.0.1, 18.0.2, or any 17.x release)
  2. Confirm the Files PDF viewer is enabled
    Navigate to the Nextcloud admin panel under Apps or Settings, locate the Files application or PDF viewer component, and verify its status shows as enabled
    Affected if The PDF viewer app or the Files app with PDF viewing capability is installed and active on the server
  3. Check if users have access to the PDF viewer
    Verify that the Files PDF viewer functionality is accessible to users by logging in as a standard user and attempting to open a PDF file through the web interface
    Affected if Users can successfully open PDF files through the Nextcloud Files interface, indicating the vulnerable component is in use

You are affected if your Nextcloud Server installation shows a version number lower than 18.0.3 and the PDF viewer feature is enabled and accessible to users.

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.

From vendor data
Upgrade available Upgrade to 18.0.3 or later
Fixed in 18.0.3
Interim mitigation

Update Nextcloud Server to a version that includes the patched PDF viewer library, or manually upgrade the underlying third-party PDF library to a version without the XSS vulnerability.

Fix this in Nextcloud Server Scoped from the published advisory
  • Consultation2.0 h
  • Implementation4.0 h
  • Testing4.0 h
  • Review / QA2.0 h
12.0 hours of engineering $2,080
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-2020-8155 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
  • No weaponised exploit code, or anything meant to cause harm
  • No spam, self-promotion, credentials, or personal data