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OnlineApplication · Collabora

CVE-2021-43817

MEDIUM · 6.1 CVSS v3.1 Published 2021-12-13
Fix available
A fix is available. Upgrade to 4.2.20 / 6.4.16 or later.
See remediation →
68/100
Remediation priority · Elevated
Remotely reachable No privileges

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
Collabora Online is a collaborative online office suite based on LibreOffice technology. In affected versions a reflected XSS vulnerability was found in Collabora Online. An attacker could inject unescaped HTML into a variable as they created the Collabora Online iframe, and execute scripts inside the context of the Collabora Online iframe. This would give access to a small set of user settings stored in the browser, as well as the session's authentication token which was also passed in at iframe creation time. Users should upgrade to Collabora Online 6.4.16 or higher or Collabora Online 4.2.20 or higher. Collabora Online Development Edition 21.11 is not affected.

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

Reflected XSS vulnerability in Collabora Online allows attackers to inject unescaped HTML into iframe parameters during iframe creation, enabling script execution within the iframe context and exposure of user settings and session authentication tokens.

MitigationUpgrade to Collabora Online 6.4.16 or higher, or 4.2.20 or higher, which contain proper HTML escaping for iframe parameters.

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
OnlineApplication
Affected:< 4.2.20>= 6.4.0, < 6.4.16

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
Changed
Confidentiality
Low
Integrity
Low
Availability
None

CVSS:3.1/AV:N/AC:L/PR:N/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. Identify if Collabora Online is installed
    Check for Collabora Online processes, Docker containers (commonly named 'collabora', 'CODE', or 'collabora-online'), or the web service listening on port 9980. Look for packages named 'collabora*' or 'libreoffice*' if installed via system package manager.
    Affected if Collabora Online is present on the system
  2. Determine installed version
    If running as Docker, run 'docker ps' and inspect the container image tag, or use 'docker inspect <container> --format "{{.Config.Image}}"'. If installed via package manager, check with 'dpkg -l | grep collabora' or 'rpm -qa | grep -i collabora'. If running as a service, check the binary or service version.
    Affected if Unable to determine the version for comparison
  3. Compare version against vulnerable ranges
    The affected version ranges are: < 4.2.20, OR >= 6.4.0 AND < 6.4.16. Compare your installed version (such as 4.2.10, 6.4.0, 6.4.15) against these ranges.
    Affected if Installed version falls within < 4.2.20 OR (>= 6.4.0 AND < 6.4.16)
  4. Verify iframe feature is accessible
    Confirm the Collabora Online web interface is reachable and iframe embedding functionality is available. This is typically used when Collabora Online is embedded via iframe in other applications (like Nextcloud, OwnCloud). Check if the URL pattern includes iframe parameters.
    Affected if Iframe embedding is used and the installed version is vulnerable

User is affected if Collabora Online is installed and the version is either below 4.2.20, or between 6.4.0 and 6.4.15 inclusive.

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 4.2.20 / 6.4.16 or later
Fixed in 4.2.206.4.16
Interim mitigation

Upgrade to Collabora Online 6.4.16 or higher, or 4.2.20 or higher, which contain proper HTML escaping for iframe parameters.

Recommended fix High confidence

Collabora Online 6.4.16 or higher (for 6.4.x branch); Collabora Online 4.2.20 or higher (for 4.x branch)

  1. Identify your current Collabora Online version by checking your installation
  2. If running version >= 6.4.0 and < 6.4.16, plan upgrade to version 6.4.16 or higher
  3. If running version < 4.2.20 (and not >= 6.4.0), plan upgrade to version 4.2.20 or higher
  4. Back up your current Collabora Online configuration and data
  5. Stop the Collabora Online service
  6. Upgrade Collabora Online using your deployment method (e.g., Docker pull, apt-get update, or your package manager)
  7. Verify the new version is installed (6.4.16+ or 4.2.20+)
  8. Restart the Collabora Online service

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

Fix this in Online Scoped from the published advisory
  • Consultation2.0 h
  • Implementation3.0 h
  • Testing2.0 h
  • Review / QA1.0 h
8.0 hours of engineering $1,420
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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-2021-43817 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