# CVE-2026-4139: mCatFilter <= 0.5.2 - Cross-Site Request Forgery via compute_post() Function

> Unauthenticated attackers can modify plugin settings via CSRF if an administrator clicks a malicious link.

- **Severity:** Medium 4.3 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:L/A:N`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** A user has to click or open something
- **Fix available:** No
- **Published:** 22 Apr 2026
- **Updated:** 22 Apr 2026
- **Also known as:** GHSA-9p67-72c6-m54h

## What is CVE-2026-4139?

CVE-2026-4139 is a medium-severity vulnerability in chsxf mCatFilter, published on 22 Apr 2026. An attacker can exploit it over the internet without logging in, and only if a user opens a file or follows a link.

### Official description

The mCatFilter plugin for WordPress is vulnerable to Cross-Site Request Forgery in all versions up to and including 0.5.2. This is due to the complete absence of nonce verification and capability checks in the compute_post() function, which processes settings updates. The compute_post() function is called in the plugin constructor on every page load via the plugins_loaded hook, and it directly processes $_POST data to modify plugin settings via update_option() without any CSRF token validation. This makes it possible for unauthenticated attackers to modify all plugin settings, including category exclusion rules, feed exclusion flags, and tag page exclusion flags, via a forged POST request, granted they can trick a site administrator into performing an action such as clicking a link.

Weakness: CWE-352 (Cross-Site Request Forgery)

## Which versions are affected by CVE-2026-4139?


## How do I fix CVE-2026-4139?

No fix has been published for CVE-2026-4139 yet. Limit exposure of the affected software until one is available.

## Is CVE-2026-4139 being exploited?

There is no known exploitation of CVE-2026-4139 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-4139 and fix it if it is affected.

What it is: CVE-2026-4139 is a medium-severity vulnerability in chsxf mCatFilter, published on 22 Apr 2026. An attacker can exploit it over the internet without logging in, and only if a user opens a file or follows a link.
Exploitation: There is no known exploitation of CVE-2026-4139 in the wild and no public exploit code.

Affected product: chsxf mCatFilter. 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-2026-4139/ (Markdown: https://insights.sbomify.com/CVE-2026-4139/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-4139
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-4139
- OSV: https://osv.dev/vulnerability/CVE-2026-4139

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-4139/
Summaries are generated and may contain mistakes; the official description above is the record.