CVE-2026-4658

Gutenberg Essential Blocks <= 6.0.4 - Authenticated (Contributor+) Stored Cross-Site Scripting via Block Attributes

2026-05-01 16:12
AlexHenry

Strategic Overview

Status
Patched in 6.1.0
Affected Plugin
Gutenberg Essential Blocks – Page Builder for Gutenberg Blocks & Patterns
Affected Version
<= 6.0.4
CVSS
6.4Medium
Weakness type
CWE-79 · Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting')
CVE
CVE-2026-4658
View all Gutenberg Essential Blocks – Page Builder for Gutenberg Blocks & Patterns vulnerabilities

At a glance

CVE-2026-4658 is a medium-severity Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting') vulnerability in the Gutenberg Essential Blocks WordPress plugin, affecting versions <= 6.0.4. It carries a CVSS score of 6.4 (reachable over the network; low attack complexity). Exploitation requires an authenticated account at Contributor level or above. The issue is fixed in version 6.1.0; sites on affected versions should update now. Disclosed May 2026, reported by AlexHenry.

Vulnerability Overview

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 Analysis

The vector marks this flaw as remotely reachable over the network, with low attack complexity — no special timing or configuration is needed, and no interaction from a victim user.

CWE-79: Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting')

Gutenberg Essential Blocks <= 6.0.4 carries this weakness at render_callback(), and reaching it takes an account at Contributor level or above. Cross-site scripting happens when input from a request is written into a page without being escaped for the context it lands in, so the browser parses attacker-supplied text as markup or script.

Injected script runs with the privileges of whoever views the affected page, which is how these flaws turn into administrator session theft, silent account creation or persistent backdoors in page content. For Gutenberg Essential Blocks the fix is 6.1.0: builds <= 6.0.4 are affected, anything from 6.1.0 onward is not.

Remediation

Update to version 6.1.0, or a newer patched version

How does WordSec protect against this?

An attacker needs Contributor access first, so the firewall sees the attempt as traffic from a logged-in account: WordSec's web application firewall inspects request payloads before WordPress loads them. None of that substitutes for the fix: Gutenberg Essential Blocks 6.1.0 closes this, and updating the plugin is the step that ends it.

  • Firewall
  • Alerts

External References

https://www.cve.org/CVERecord?id=CVE-2026-4658https://www.wordfence.com/threat-intel/vulnerabilities/id/3e7eed9d-2d44-4951-b66b-7d8995ca617dhttps://nvd.nist.gov/vuln/detail/CVE-2026-4658

Related records

Vulnerability data © Defiant, Inc., provided under the Wordfence Intelligence T&C