Craft CMS: Authenticated RCE via `condition.config` JSON cleanse bypass

Overview

Craft CMS has an authenticated remote code execution issue in the control panel element-search condition handling.

Craft cleans the outer request-controlled condition array with Component::cleanseConfig(), but Conditions::createCondition() later decodes and merges the JSON string in condition.config without re-running cleanseConfig() on the decoded/merged configuration.

Because condition.config is a JSON string during the first cleanse, Yii special config keys such as as ... and on ... can be hidden inside it. After JSON decoding, those keys reach FieldLayout object creation and are interpreted by Yii as behavior/event configuration.

The RCE is semi-blind: the trigger endpoint returns a normal JSON response, and the command output is verified via a server-side file-write side effect retrieved in a subsequent request.

Preconditions

• The attacker needs an authenticated Craft control panel session.
• A valid CSRF token is required.

Impact

An authenticated control panel user can inject Yii behavior/event configuration after Craft’s intended config cleanse boundary. In the confirmed local lab, this led to command execution as the PHP/web user.

Potential attacker impact:

• Execute operating system commands as the PHP/web user.
• Read Craft secrets, environment variables, and application configuration.
• Access database credentials and stored site content.
• Modify site content, users, and application state.
• Pivot to internal services reachable from the Craft host or container.
• Cause denial of service or establish persistence depending on deployment permissions.

Affected packages

• craftcms/cms >= 5.0.0-RC1, < 5.10.6
• craftcms/cms >= 4.0.0-RC1, < 4.18.2

Remediation

Upgrade to a patched release:

• craftcms/cms 5.10.6
• craftcms/cms 4.18.2