# CVE-2026-16558: YMC Filter < 3.12.8 - Contributor+ Stored XSS via Layout Builder Schema

> Contributors can inject malicious JavaScript into YMC Filter settings, leading to stored XSS attacks against site visitors.

- **Severity:** Medium 5.4 (`CVSS:3.1/AV:N/AC:L/PR:L/UI:R/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:** A user has to click or open something
- **Fix available:** No
- **Published:** 8 Aug 2026
- **Updated:** 10 Aug 2026
- **Also known as:** GHSA-p3q7-6w8f-v63h

## What is CVE-2026-16558?

CVE-2026-16558 is a medium-severity cross-site scripting vulnerability in Unknown YMC Filter, published on 8 Aug 2026. Any signed-in user can exploit it over the network, and only if a user opens a file or follows a link.

### Official description

The YMC Filter WordPress plugin before 3.12.8 does not sanitize and escape a layout builder setting before outputting it on a public endpoint, and does not verify object ownership when the setting is saved, allowing users with the Contributor role and above to store JavaScript that executes in the browser of any visitor viewing an affected filter.

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

## Which versions are affected by CVE-2026-16558?


## How do I fix CVE-2026-16558?

No fix has been published for CVE-2026-16558 yet. Limit exposure of the affected software until one is available.

## Is CVE-2026-16558 being exploited?

It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-16558 exists.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-16558 and fix it if it is affected.

What it is: CVE-2026-16558 is a medium-severity cross-site scripting vulnerability in Unknown YMC Filter, published on 8 Aug 2026. Any signed-in user can exploit it over the network, and only if a user opens a file or follows a link.
Exploitation: It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-16558 exists.

Affected product: Unknown YMC Filter. 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-2026-16558/ (Markdown: https://insights.sbomify.com/CVE-2026-16558/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-16558
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-16558
- OSV: https://osv.dev/vulnerability/CVE-2026-16558

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From sbomify Insights: https://insights.sbomify.com/CVE-2026-16558/
Summaries are generated and may contain mistakes; the official description above is the record.