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MagentoCMS · Openmage

CVE-2021-21426

CRITICAL · 9.8 CVSS v3.1 Published 2021-04-21
Fix available
A fix is available. Upgrade to 19.4.13 / 20.0.9 or later.
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
Magento-lts is a long-term support alternative to Magento Community Edition (CE). In magento-lts versions 19.4.12 and prior and 20.0.8 and prior, there is a vulnerability caused by the unsecured deserialization of an object. A patch in versions 19.4.13 and 20.0.9 was back ported from Zend Framework 3. The vulnerability was assigned CVE-2021-3007 in Zend Framework.

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

Magento-lts versions 19.4.12 and prior and 20.0.8 and prior contain an insecure deserialization vulnerability that allows remote code execution through unsafe object deserialization. This vulnerability was originally identified in Zend Framework (CVE-2021-3007) and backported fixes were released in versions 19.4.13 and 20.0.9.

MitigationUpgrade Magento-lts to version 19.4.13 or later (for the 19.x branch) or version 20.0.9 or later (for the 20.x branch) to apply the patch that addresses the insecure deserialization. If immediate upgrade is not possible, audit code for PHP unserialize() calls without proper validation.

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
MagentoCMS
Affected:< 19.4.13>= 20.0.0, < 20.0.9

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
Unchanged
Confidentiality
High
Integrity
High
Availability
High

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/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. Locate Magento-lts installation directory
    Identify the root directory where Magento-lts is installed. This is typically the document root for the web server.
    Affected if Cannot locate the installation to perform version checking
  2. Find the installed Magento-lts version
    Check the composer.json file in the installation root for the 'version' field, or look for a version.php file in app/etc/ directory. The version may also be visible in the Magento admin panel footer.
    Affected if Version is less than 19.4.13 for 19.x branch, or less than 20.0.9 for 20.x branch, or any version >= 20.0.0 but < 20.0.9
  3. Identify PHP unserialize() usage
    Search the codebase for 'unserialize(' calls, particularly in vendor/zendframework or custom code that handles serialized data from user input. Use: grep -r "unserialize(" --include="*.php" .
    Affected if unserialize() calls exist without prior validation or use of JSON instead of PHP serialization
  4. Check for Zend Framework component
    Examine the vendor/zendframework directory for the presence of zend-serializer or zend-cache components that contain the vulnerable deserialization logic.
    Affected if Zend Framework deserialization components are present and unpatched

You are affected if your installed Magento-lts version is below 19.4.13 (19.x branch) or below 20.0.9 (20.x branch) and the codebase contains unserialize() calls that handle untrusted data.

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 19.4.13 / 20.0.9 or later
Fixed in 19.4.1320.0.9
Interim mitigation

Upgrade Magento-lts to version 19.4.13 or later (for the 19.x branch) or version 20.0.9 or later (for the 20.x branch) to apply the patch that addresses the insecure deserialization. If immediate upgrade is not possible, audit code for PHP unserialize() calls without proper validation.

Recommended fix High confidence

Magento-lts 19.4.13 or 20.0.9 (whichever branch applies)

  1. 1. Backup your Magento-lts database and files completely
  2. 2. Review the Magento-lts upgrade documentation for your current version
  3. 3. Upgrade to Magento-lts version 19.4.13 (if on the 19.x branch) or version 20.0.9 (if on the 20.x branch)
  4. 4. Run any required database migration scripts after upgrading
  5. 5. Clear all caches (var/cache, var/generation, etc.)
  6. 6. Verify the application is functioning correctly after upgrade
  7. 7. Test that the deserialization vulnerability is no longer present
Caveat Review Magento-lts release notes for any breaking changes between your current version and 19.4.13/20.0.9; ensure compatibility with your PHP version and extensions

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

Fix this in Magento Scoped from the published advisory
  • Consultation3.0 h
  • Implementation6.0 h
  • Testing6.0 h
  • Review / QA3.0 h
18.0 hours of engineering $3,120
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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-2021-21426 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