NiceHash Miner Excavator API Cross-Site Request Forgery
=======================================================
The latest version of this advisory is available at:
https://sintonen.fi/advisories/nicehash-miner-excavator-api-csrf.txt


Overview
--------

NiceHash Miner Excavator plugin contains a vulnerability that enables any external
web site to send commands to the local miner instance, and to redirect the mined
coins to arbitrary mining address.


Description
-----------

NiceHash Miner Excavator plugin uses a local JSON API at localhost:4000. External
javascript (any website browsed by the victim) can craft and send JSON requests to
the API endpoint by employing XMLHTTPRequest objects.


Impact
------

Malicious website can command the NiceHash Excavator miner to send the coins to
an arbitrary mining address, effectively stealing the mined coins.


Details
-------

The discovered vulnerability, described in more detail below, enables the attack
described here in brief.

1. The attacker creates a JavaScript payload that uses XMLHTTPRequest object to
   send JSON API commands to localhost:4000 API endpoint. Note that the API
   expects a raw TCP connection but since the parser is relaxed, it will skip any
   non-JSON input such as the GET line and the HTTP header lines until the actual
   HTTP POST data is met. Additionally since there is no need to specify a
   Content-Type for the request, no Cross-Origin Resource Sharing preflight check
   is needed or performed. The payload uses the 'subscribe' API method to connect
   the miner to the attacker's mining address. The payload then uses
   'cmdfile.commit' method to make the address change persistent.

2. The victim running the NiceHash Miner Excavator plugin browses to the site
   hosting the malicious JavaScript payload. The payload activates and redirects
   NiceHash Miner to send the mined coins to the attacker's mining address.

3. By targetting a wide audience of users running NiceHash Excavator Miner, the
   attacker could acquire thousands of miners, resulting in huge profits.


Vulnerabilities
---------------

1. CWE-20: Improper Input Validation

The root cause for the vulnerability is the lax input validation of the Excavator
TCP API endpoint. The API will consume newline terminated lines arriving to the
API endpoint and merely skip invalid lines. This enables the attack to work via
regular HTTP requests, effectively enabling the Cross-Site Request Forgery attack.


Vulnerable versions
-------------------

The following product versions are vulnerable:

- NiceHash Excavator plugin up to and including version 1.6.7c.


End user recommendations
------------------------

1. Upgrade to the NiceHash Miner 3.0.6.5 or later.


Credits
-------

The vulnerability was discovered by Harry Sintonen / F-Secure Consulting.


Timeline
--------

2021.03.28  discovered the vulnerability
2021.03.28  wrote a proof of concept exploit
2021.03.28  contacted NiceHash over security@nicehash.com
2021.03.28  wrote the first draft of this advisory
2021.03.28  sent the advisory to security@nicehash.com
2021.03.29  Excavator plugin 1.6.11a released. this version switched to
            HTTP JSON API (-wp 4000)
2021.04.02  reminded security@nicehash.com that -wp 4000 alone doesn't resolve
            the issue
2021.04.15  NiceHash Miner 3.0.6.5 released, fixing the vulnerability
2021.05.14  public disclosure