# CVE-2026-8981: Lazy Blocks < 4.3.0 - Admin+ Stored XSS via Custom Block Frontend HTML

> Administrators can inject arbitrary JavaScript into block templates, leading to stored XSS for site visitors.

- **Severity:** Low 3.5 (`CVSS:3.1/AV:N/AC:L/PR:H/UI:R/S:U/C:L/I:L/A:N`)
- **Exploited in the wild:** Not known
- **Login needed:** An administrator
- **Attackable:** Over the internet
- **Victim action needed:** A user has to click or open something
- **Fix available:** No
- **Published:** 9 Jun 2026
- **Updated:** 9 Jun 2026
- **Also known as:** GHSA-cfcv-65jq-76jw

## What is CVE-2026-8981?

CVE-2026-8981 is a low-severity cross-site scripting vulnerability in Unknown Custom Block Builder, published on 9 Jun 2026. An attacker needs administrator access to exploit it, and only if a user opens a file or follows a link.

### Official description

The Custom Block Builder  WordPress plugin before 4.3.0 does not consistently check the unfiltered_html capability across all paths that write to its block template code fields, allowing administrators on multisite installations (or single-site installs with DISALLOW_UNFILTERED_HTML defined) to inject arbitrary JavaScript that executes for any visitor of pages embedding the affected block.

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

## Which versions are affected by CVE-2026-8981?


## How do I fix CVE-2026-8981?

No fix has been published for CVE-2026-8981 yet. Limit exposure of the affected software until one is available.

## Is CVE-2026-8981 being exploited?

There is no known exploitation of CVE-2026-8981 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-8981 and fix it if it is affected.

What it is: CVE-2026-8981 is a low-severity cross-site scripting vulnerability in Unknown Custom Block Builder, published on 9 Jun 2026. An attacker needs administrator access to exploit it, and only if a user opens a file or follows a link.
Exploitation: There is no known exploitation of CVE-2026-8981 in the wild and no public exploit code.

Affected product: Unknown Custom Block Builder. 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-2026-8981/ (Markdown: https://insights.sbomify.com/CVE-2026-8981/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-8981
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-8981
- OSV: https://osv.dev/vulnerability/CVE-2026-8981

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From sbomify Insights: https://insights.sbomify.com/CVE-2026-8981/
Summaries are generated and may contain mistakes; the official description above is the record.