# CVE-2026-84999: Pie Register Premium <= 3.8.4.0 - Unauthenticated Arbitrary File Upload via piereg_file_upload AJAX Handler


- **Severity:** Critical 9.8 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H`)
- **Exploited in the wild:** Not known
- **Fix available:** No
- **Published:** 28 Oct 2026
- **Updated:** 29 Oct 2026
- **Also known as:** GHSA-356m-cxhj-j59p

## What is CVE-2026-84999?

CVE-2026-84999 is a critical vulnerability in Pie Register Premium, published on 28 Oct 2026. 

### Official description

The Pie Register Premium plugin for WordPress is vulnerable to Unrestricted File Type Upload in all versions up to, and including, 3.8.4.0 via the piereg_file_upload function. This is due to the plugin performing file type validation via wp_check_filetype and wp_check_filetype_and_ext but never checking whether those validation calls produced errors before move_uploaded_file() is called, combined with no nonce or capability check on the AJAX handler. This makes it possible for unauthenticated attackers to upload files of dangerous types (e.g. PHP scripts) that may be executable, which makes remote code execution possible. The server returns the generated destination filename in the response, giving the attacker the exact path needed to trigger the uploaded file.

Weakness: CWE-434 (Unrestricted Upload of File with Dangerous Type)

## Which versions are affected by CVE-2026-84999?


## How do I fix CVE-2026-84999?

No fix has been published for CVE-2026-84999 yet. Limit exposure of the affected software until one is available.

## Is CVE-2026-84999 being exploited?

There is no known exploitation of CVE-2026-84999 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-84999 and fix it if it is affected.

What it is: CVE-2026-84999 is a critical vulnerability in Pie Register Premium, published on 28 Oct 2026. 
Exploitation: There is no known exploitation of CVE-2026-84999 in the wild and no public exploit code.

Affected product: Pie Register Premium. 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-2026-84999/ (Markdown: https://insights.sbomify.com/CVE-2026-84999/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-84999
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-84999
- OSV: https://osv.dev/vulnerability/CVE-2026-84999

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-84999/
Summaries are generated and may contain mistakes; the official description above is the record.