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Cross-site Scripting (XSS)Weakness · CWE-79

CVE-2026-4658

MEDIUM · 6.4 CVSS v3.1 Published 2026-05-02
Mitigation only
No fix yet — a mitigation exists. There is no fixed release. A documented workaround reduces exposure in the meantime.
See remediation →
70/100
Remediation priority · Elevated
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 Essential Blocks – Page Builder Gutenberg Blocks, Patterns & Templates plugin for WordPress is vulnerable to Stored Cross-Site Scripting via the className, classHook, and blockId attributes in the Add to Cart block (essential-blocks/add-to-cart) in all versions up to, and including, 6.0.4. This is due to insufficient output escaping in the render_callback() function where these attributes are placed into class and data-id HTML attributes using raw sprintf() and implode() without esc_attr() escaping. While the outer wrapper div uses get_block_wrapper_attributes() which properly escapes, the inner divs do not. This makes it possible for authenticated attackers, with Contributor-level access and above, to inject arbitrary web scripts in pages that will execute whenever a user accesses an injected page.

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 Essential Blocks WordPress plugin fails to properly escape the className, classHook, and blockId attributes in its Add to Cart block's render_callback() function. These values are inserted directly into HTML class and data-id attributes via sprintf() and implode() without esc_attr() escaping, allowing authenticated attackers with Contributor-level access to inject malicious JavaScript that executes when users view affected pages.

MitigationUpdate the plugin to version 6.0.5 or later, which should include proper esc_attr() escaping for these attributes in the render_callback() function.

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
Changed
Confidentiality
Low
Integrity
Low
Availability
None

CVSS:3.1/AV:N/AC:L/PR:L/UI:N/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. Verify Essential Blocks plugin is installed
    In WordPress admin, go to Plugins > Installed Plugins and look for 'Essential Blocks' in the list. Alternatively, check the /wp-content/plugins/essential-blocks/ directory exists.
    Affected if The plugin is installed and active in the WordPress environment
  2. Identify the installed version of Essential Blocks
    In WordPress admin, go to Plugins > Installed Plugins and click on 'View details' for Essential Blocks to see the version number. Or check the plugin's main PHP file header for the Version field.
    Affected if The version is lower than 6.0.5 (the fixed version)
  3. Confirm Add to Cart block is in use
    Check pages, posts, or templates where the Essential Blocks Add to Cart block has been added. This can be done via the WordPress block editor or by searching the database wp_posts table for content containing 'wp:essential-blocks/add-to-cart' or similar block markup.
    Affected if The Add to Cart block from Essential Blocks is present on any published content
  4. Inspect render_callback for missing escaping
    Locate the Add to Cart block's render_callback function in the plugin files (typically in /wp-content/plugins/essential-blocks/blocks/add-to-cart/). Search for sprintf() or implode() calls that construct class or data-id attributes using className, classHook, or blockId variables without esc_attr() wrapping.
    Affected if The code shows these attributes being inserted without esc_attr() escaping

The environment is affected if Essential Blocks plugin versions below 6.0.5 are installed, the Add to Cart block is used on any page, and the render_callback lacks esc_attr() on className, classHook, or blockId attributes.

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

Update the plugin to version 6.0.5 or later, which should include proper esc_attr() escaping for these attributes in the render_callback() function.

Have this fixed Scoped from the published advisory
  • Consultation2.0 h
  • Implementation1.0 h
  • Testing2.0 h
  • Review / QA1.0 h
6.0 hours of engineering $1,060
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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-2026-4658 in production — separate from our analysis above.

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What this is

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What belongs here
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  • Version or environment caveats, and links to real fixes
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