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OS Command InjectionWeakness · CWE-78

CVE-2021-47667

CRITICAL · 10.0 CVSS v3.1 Published 2025-04-05
Mitigation only
No fix yet — a mitigation exists. There is no fixed release. A documented workaround reduces exposure in the meantime.
See remediation →
100/100
Remediation priority · Urgent
Remotely reachable No privileges Zero-click

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 OS command injection vulnerability in lib/NSSDropoff.php in ZendTo 5.24-3 through 6.x before 6.10-7 allows unauthenticated remote attackers to execute arbitrary commands via shell metacharacters in the tmp_name parameter when dropping off a file via a POST /dropoff request.

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

A command injection vulnerability exists in ZendTo's file upload functionality. The lib/NSSDropoff.php script fails to sanitize the tmp_name parameter passed during a POST /dropoff request, allowing attackers to inject shell metacharacters and execute arbitrary OS commands without authentication.

MitigationUpgrade ZendTo to version 6.10-7 or later. If immediate patching is not possible, implement web application firewall rules to block requests with shell metacharacters in upload parameters.

Verify against the referenced sources before acting — the references below are authoritative for this CVE, this summary is not.

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
None
Scope
Changed
Confidentiality
High
Integrity
High
Availability
High

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:H/A:H

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 ZendTo is installed
    Search for ZendTo directories or check web server document roots for ZendTo files such as NSSDropoff.php, index.php, or the vendor directory. Common locations include /var/www/zendto, /opt/zendto, or within the web server's htdocs folder.
    Affected if ZendTo software is found running on the system
  2. Determine the installed ZendTo version
    Locate and read the version file or check the main index.php for version strings. Alternatively, check the changelog or RELEASE_NOTES file in the ZendTo installation directory.
    Affected if The installed version is earlier than 6.10-7 (the fixed release)
  3. Verify the dropoff endpoint is accessible
    Test if the /dropoff endpoint is reachable by making a GET request to the ZendTo server on port 80 or 443, or by checking the web server configuration for routes pointing to NSSDropoff.php.
    Affected if The dropoff functionality is enabled and accessible via web
  4. Confirm NSSDropoff.php exists and is executable
    Locate the lib/NSSDropoff.php file within the ZendTo installation and verify it exists. Check file permissions to confirm it can be executed by the web server.
    Affected if The vulnerable NSSDropoff.php script is present and web-accessible

A user is affected if ZendTo is installed, running a version earlier than 6.10-7, and the dropoff upload feature is accessible via the web interface.

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
Mitigation available No clean upgrade yet — mitigate in the meantime
Mitigation

Upgrade ZendTo to version 6.10-7 or later. If immediate patching is not possible, implement web application firewall rules to block requests with shell metacharacters in upload parameters.

Recommended fix Moderate confidence

ZendTo 6.10-7 or later

  1. 1. Identify the current ZendTo version by checking the version file or admin interface
  2. 2. Backup the current ZendTo installation and database before upgrading
  3. 3. Download ZendTo version 6.10-7 or later from the official source
  4. 4. Install the upgrade following the standard ZendTo upgrade procedure
  5. 5. Verify the upgrade was successful by checking the version number
  6. 6. Test that file dropoff functionality works correctly
  7. 7. Confirm the lib/NSSDropoff.php file has been updated to the fixed version

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

Have this fixed Scoped from the published advisory
  • Consultation2.0 h
  • Implementation2.0 h
  • Testing2.0 h
  • Review / QA1.0 h
7.0 hours of engineering $1,240
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An estimate, not a bill — we confirm scope with you before any work starts. Need it this week? Rush from $1,984.

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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-2021-47667 in production — separate from our analysis above.

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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
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