# CVE-2026-4658: Gutenberg Essential Blocks <= 6.0.4 - Authenticated (Contributor+) Stored Cross-Site Scripting via Block Attributes

> Authenticated attackers with Contributor access can inject arbitrary scripts via block attributes, leading to stored XSS execution on victim pages.

- **Severity:** Medium 6.4 (`CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:L/I:L/A:N`)
- **Exploited in the wild:** Not known
- **Login needed:** Any signed-in user
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** No
- **Published:** 2 May 2026
- **Updated:** 4 May 2026
- **Also known as:** GHSA-5vvh-659m-gjm3

## What is CVE-2026-4658?

CVE-2026-4658 is a medium-severity cross-site scripting vulnerability in wpdevteam Gutenberg Essential Blocks – Page Builder for Gutenberg Blocks & Patterns, published on 2 May 2026. Any signed-in user can exploit it over the network, with no action from the victim.

### Official description

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.

Weakness: CWE-79 (Improper Neutralization of Input During Web Page Generation)

## Which versions are affected by CVE-2026-4658?


## How do I fix CVE-2026-4658?

No fix has been published for CVE-2026-4658 yet. Limit exposure of the affected software until one is available.

## Is CVE-2026-4658 being exploited?

There is no known exploitation of CVE-2026-4658 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-4658 and fix it if it is affected.

What it is: CVE-2026-4658 is a medium-severity cross-site scripting vulnerability in wpdevteam Gutenberg Essential Blocks – Page Builder for Gutenberg Blocks & Patterns, published on 2 May 2026. Any signed-in user can exploit it over the network, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2026-4658 in the wild and no public exploit code.

Affected product: wpdevteam Gutenberg Essential Blocks – Page Builder for Gutenberg Blocks & Patterns. No package-level version data is available, so check the vendor advisory linked from the reference page.

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-4658/ (Markdown: https://insights.sbomify.com/CVE-2026-4658/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-4658
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-4658
- OSV: https://osv.dev/vulnerability/CVE-2026-4658

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From sbomify Insights: https://insights.sbomify.com/CVE-2026-4658/
Summaries are generated and may contain mistakes; the official description above is the record.