# CVE-2026-86730: Craft CMS 5.0.0-RC1 before 5.10.12 Behavior Injection RCE

> Authenticated Craft CMS users can inject Yii2 behaviors via field layouts to achieve remote code execution.

- **Severity:** High 8.7 (`CVSS:4.0/AV:N/AC:L/AT:N/PR:L/UI:N/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N`)
- **Exploited in the wild:** Not known
- **Login needed:** Any signed-in user
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** No
- **Published:** 8 Sep 2026
- **Updated:** 8 Sep 2026
- **Also known as:** GHSA-j4wp-xfvq-c8f7, GHSA-qj4v-m29p-fj4m

## What is CVE-2026-86730?

CVE-2026-86730 is a high-severity code injection vulnerability in craftcms cms, published on 8 Sep 2026. Any signed-in user can exploit it over the network, with no action from the victim.

### Official description

Craft CMS versions before 5.10.12 fail to properly cleanse string-typed field-layout elements, allowing authenticated control-panel users to inject Yii2 behavior attachments and event handlers. Attackers can post field-layout tab elements as JSON strings to bypass cleanse validation, then trigger arbitrary object instantiation and code execution through Craft::createObject().

Weakness: CWE-94 (Improper Control of Generation of Code)

## Which versions are affected by CVE-2026-86730?


## How do I fix CVE-2026-86730?

No fix has been published for CVE-2026-86730 yet. Limit exposure of the affected software until one is available.

## Is CVE-2026-86730 being exploited?

There is no known exploitation of CVE-2026-86730 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-86730 and fix it if it is affected.

What it is: CVE-2026-86730 is a high-severity code injection vulnerability in craftcms cms, published on 8 Sep 2026. Any signed-in user can exploit it over the network, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2026-86730 in the wild and no public exploit code.

Affected product: craftcms cms. 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-2026-86730/ (Markdown: https://insights.sbomify.com/CVE-2026-86730/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-86730
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-86730
- OSV: https://osv.dev/vulnerability/CVE-2026-86730

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-86730/
Summaries are generated and may contain mistakes; the official description above is the record.