SafeURL for Python

Note: The SafeURL libraries are no longer maintained and we recommend considering other SSRF mitigation approaches alongside application-layer SSRF protection libraries. See our 2023 blog post for more details.

Ported by @nicolasrod and docs by @momopranto

Overview

SafeURL is a library that aids developers in protecting against a class of vulnerabilities known as Server Side Request Forgery (SSRF). It does this by validating each part of the URL against a configurable white or black list before making an HTTP request. SafeURL is open-source and licensed under MIT.

Note that for mitigating SSRF vulnerabilities, we first recommend routing outbound requests from your infrastructure through a proxy such as Smokescreen. Alternately, ensure that all services which can make outbound requests to potentially user-controlled URLs are firewalled from talking to other internal hosts. Application-layer defences such as this library should only be used if those options are not practical. Please see our blog post for further information.

Installation

Clone this repository and import it into your project.

Implementation

SafeURL serves as a replacement wrapper for PyCurl in Python.

try:
  #User controlled input
  url = request.args['url']
  su = safeurl.SafeURL()
  #Execute using SafeURL
  res = su.execute(url)
except:
  print "Unexpected error:", sys.exc_info()
  #URL wasn't safe

Configuration

Options such as white and black lists can be modified. For example:

try:
    su = safeurl.SafeURL()
    #Create an options object
    opt = safeurl.Options()
    opt.clearList("whitelist")
    opt.clearList("blacklist")
    #Allow requests to specific domains
    opt.setList("whitelist", ["google.com", "youtube.com"], "domain")
    #Restrict urls with the ftp scheme
    opt.setList("blacklist",["ftp"],"scheme")

    su.setOptions(opt)
    res = su.execute("http://www.youtube.com")
except:
    print "Unexpected error:", sys.exc_info()