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Deserialization of Untrusted DataWeakness · CWE-502

CVE-2026-8365

HIGH · 8.8 CVSS v3.1 Published 2026-06-09
Mitigation only
No fix yet — a mitigation exists. There is no fixed release. A documented workaround reduces exposure in the meantime.
See remediation →
94/100
Remediation priority · Urgent
Remotely reachable 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
The Blocksy theme for WordPress is vulnerable to PHP Object Injection leading to Remote Code Execution via the 'blocksy_meta' REST API field and the V200 database migration in versions up to and including 2.1.35. This is due to insufficient input sanitization in the blocksy_sanitize_post_meta_options() function, which only blocks values containing '<' or '>' and does not prevent serialized PHP object strings from being stored in post meta, combined with the SearchReplacer::run_recursively() function unconditionally deserializing all string values via @unserialize() during migration without restricting allowed classes. This makes it possible for authenticated attackers, with contributor-level access and above, to inject a serialized Blocksy\RaiiPattern object into post meta that, when the V200 migration runs on an upgraded site, is deserialized and triggers RaiiPattern::__destruct(), which executes arbitrary PHP callables via call_user_func().

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

The Blocksy theme for WordPress versions up to 2.1.35 have a PHP Object Injection vulnerability. The blocksy_sanitize_post_meta_options() function only filters values containing '<' or '>' characters, failing to block serialized PHP objects. Combined with the SearchReplacer::run_recursively() function that unconditionally deserializes strings via @unserialize() without restricting allowed classes, this allows authenticated attackers with contributor-level access to inject a serialized Blocksy\RaiiPattern object into post meta. When the V200 migration runs, this object is deserialized, triggering RaiiPattern::__destruct() which executes arbitrary PHP callables via call_user_func().

MitigationUpgrade Blocksy theme to version 2.1.36 or later which implements proper input sanitization and restricts unserialize() to allowed classes. If immediate upgrade is not possible, disable contributor-level API access and monitor for suspicious post meta entries.

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
Low
User interaction
None
Scope
Unchanged
Confidentiality
High
Integrity
High
Availability
High

CVSS:3.1/AV:N/AC:L/PR:L/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. Identify Blocksy theme version
    Check the theme's style.css file in wp-content/themes/blocksy/ for the 'Version:' header, or query via WordPress REST API at /wp-json/wp/v2/themes?status=active
    Affected if Version is 2.1.35 or lower
  2. Verify blocksy_meta REST API endpoint accessibility
    Test access to the /wp-json/blocksy/v1/meta endpoint using a contributor-level user account credentials via POST request
    Affected if Endpoint returns 200 OK and accepts post meta data for contributor-level authentication
  3. Confirm database migration V200 status
    Query wp_options table for a setting named 'blocksy_migration_version' or similar, or inspect wp_postmeta table for any meta_key starting with 'blocksy_' containing serialized PHP data (look for 'O:' or 'C:' patterns)
    Affected if Migration version is below V200 or serialized objects exist in blocksy post meta fields
  4. Check for Blocksy RaiiPattern objects in post meta
    Search wp_postmeta for any meta_value containing the string 'Blocksy\RaiiPattern' or examine serialized data patterns (O:... or C:... with 'RaiiPattern' class name)
    Affected if Serialized Blocksy\RaiiPattern objects are present in any blocksy_ prefixed post meta entries

User is affected if Blocksy theme version is 2.1.35 or lower AND contributor-level users have access to the blocksy_meta REST API endpoint AND the V200 migration has processed serialized data in post meta fields.

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 Blocksy theme to version 2.1.36 or later which implements proper input sanitization and restricts unserialize() to allowed classes. If immediate upgrade is not possible, disable contributor-level API access and monitor for suspicious post meta entries.

Recommended fix Moderate confidence

Latest stable release of Blocksy theme (check themes.trac.wordpress.org for the most current version)

  1. Check the currently installed Blocksy theme version in WordPress under Appearance > Themes
  2. Visit the official Blocksy theme page or WordPress theme repository to identify the latest stable release
  3. Update the Blocksy theme to the latest available version
  4. After updating, verify the site still functions correctly and review theme settings
Caveat Minor theme setting adjustments may be needed after upgrade; always backup before updating

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

Have this fixed Scoped from the published advisory
  • Consultation3.0 h
  • Implementation6.0 h
  • Testing3.0 h
  • Review / QA2.0 h
14.0 hours of engineering $2,490
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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-2026-8365 in production — separate from our analysis above.

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What this is

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What belongs here
  • Verified mitigations, workarounds, and config changes
  • Version or environment caveats, and links to real fixes
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