Jenkins cli Ampersand Replacement Arbitrary File Read

Description

This module utilizes the Jenkins cli protocol to run the `help` command. The cli is accessible with read-only permissions by default, which are all thats required.

Jenkins cli utilizes `args4j's` `parseArgument`, which calls `expandAtFiles` to replace any `@<filename>` with the contents of a file. We are then able to retrieve the error message to read up to the first two lines of a file.

Exploitation by hand can be done with the cli, see markdown documents for additional instructions.

There are a few exploitation oddities: 1. The injection point for the `help` command requires 2 input arguments. When the `expandAtFiles` is called, each line of the `FILE_PATH` becomes an input argument. If a file only contains one line, it will throw an error: `ERROR: You must authenticate to access this Jenkins.` However, we can pad out the content by supplying a first argument. 2. There is a strange timing requirement where the `download` (or first) request must get to the server first, but the `upload` (or second) request must be very close behind it. From testing against the docker image, it was found values between `.01` and `1.9` were viable. Due to the round trip time of the first request and response happening before request 2 would be received, it is necessary to use threading to ensure the requests happen within rapid succession.

Files of value: * /var/jenkins_home/secret.key * /var/jenkins_home/secrets/master.key * /var/jenkins_home/secrets/initialAdminPassword * /etc/passwd * /etc/shadow * Project secrets and credentials * Source code, build artifacts