# CVE-2026-18391: WooCommerce Subscriptions < 9.1.0 - Unauthenticated RCE via PHP Object Injection

> Unauthenticated attackers can achieve remote code execution via PHP object injection in WooCommerce Subscriptions when High-Performance Order Storage is enabled.

- **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
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** No
- **Published:** 12 Aug 2026
- **Updated:** 12 Aug 2026
- **Also known as:** GHSA-5736-34m2-3cxc

## What is CVE-2026-18391?

CVE-2026-18391 is a critical unsafe deserialization vulnerability in Unknown WooCommerce Subscriptions, published on 12 Aug 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

The WooCommerce Subscriptions WordPress plugin before 9.1.0 does not validate user input before unserializing it on stores with High-Performance Order Storage enabled, leading to a PHP Object Injection issue which unauthenticated users can escalate to Remote Code Execution via a gadget chain present in the bundled dependencies.

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

## Which versions are affected by CVE-2026-18391?


## How do I fix CVE-2026-18391?

No fix has been published for CVE-2026-18391 yet. Limit exposure of the affected software until one is available.

## Is CVE-2026-18391 being exploited?

It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-18391 exists.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-18391 and fix it if it is affected.

What it is: CVE-2026-18391 is a critical unsafe deserialization vulnerability in Unknown WooCommerce Subscriptions, published on 12 Aug 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Exploitation: It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-18391 exists.

Affected product: Unknown WooCommerce Subscriptions. 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-2026-18391/ (Markdown: https://insights.sbomify.com/CVE-2026-18391/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-18391
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-18391
- OSV: https://osv.dev/vulnerability/CVE-2026-18391

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-18391/
Summaries are generated and may contain mistakes; the official description above is the record.