Kobold hosts several services behind an Nginx reverse proxy, including an MCPJam inspector instance, a PrivateBin paste site, and an Arcane Docker management panel. I’ll exploit an unauthenticated remote code execution vulnerability in MCPJam that stems from it binding to all interfaces and installing an attacker-controlled MCP server, getting a shell. From there I’ll abuse a local file inclusion in PrivateBin’s template-selection feature, writing a PHP webshell into a host directory that is mounted into the PrivateBin container to get execution inside it. The container’s configuration leaks a database password that I’ll reuse to log into Arcane. With control over the Docker panel, I’ll create a container that mounts the host filesystem, drop an SSH key for root, and log in to take over the box.

0xdf hacks stuff

A walkthrough of the HackTheBox machine 'Kobold', which hosts MCPJam inspector, PrivateBin, and Arcane Docker management behind Nginx. Initial access is gained via CVE-2026-23744, an unauthenticated RCE in MCPJam that binds to all interfaces and allows installing an attacker-controlled MCP server. Lateral movement exploits CVE-2025-64714, a local file inclusion in PrivateBin's template-selection cookie feature, used to write and execute a PHP webshell inside the container. The container's config leaks a database password reused for Arcane. Docker panel access enables mounting the host filesystem in a new container, dropping an SSH key, and gaining root. A bonus section covers an unintended path via a misconfigured gshadow file granting ben docker group access directly.

HTB: Kobold