Class: Scryer::Rules::SsrfRule

Inherits:
Scryer::Rule show all
Defined in:
lib/scryer/rules/ssrf_rule.rb

Overview

Flags an outbound HTTP call (Net::HTTP, URI.open/bare open via open-uri, HTTParty, Faraday, RestClient) where an argument references params directly — the request's destination is user-controlled, which lets an attacker make the server issue requests to internal services, cloud metadata endpoints, or anywhere else on its network (server-side request forgery).

Constant Summary collapse

DANGEROUS_CALLS = 
{
  "Net::HTTP" => %w[get get_response post post_form],
  "URI" => %w[open],
  "HTTParty" => %w[get post put delete],
  "Faraday" => %w[get post put delete],
  "RestClient" => %w[get post put delete]
}.freeze

Instance Attribute Summary

Attributes inherited from Scryer::Rule

#file, #sexp, #source

Instance Method Summary collapse

Methods inherited from Scryer::Rule

inherited, #initialize

Constructor Details

This class inherits a constructor from Scryer::Rule

Instance Method Details

#scan ⇒ Object 



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# File 'lib/scryer/rules/ssrf_rule.rb', line 23

def scan
  findings = []

  Ast.each_node(sexp) do |node|
    next unless Ast.tagged?(node, :method_add_arg, :command, :command_call)

    inner = Ast.tagged?(node, :method_add_arg) ? node[1] : node
    receiver_and_name = Ast.call_name(inner)
    next unless receiver_and_name

    receiver, method_name = receiver_and_name
    next unless dangerous_call?(receiver, method_name)

    args = Ast.call_arguments(node)
    next unless args.any? { |a| Ast.references_params?(a) }

    line = Ast.line_of(node)
    findings << finding(
      line: line,
      message: "`#{describe_call(receiver, method_name)}` is called with a URL/argument " \
                "that references `params` — the server can be made to issue a request to " \
                "any host an attacker chooses, including internal services and cloud " \
                "metadata endpoints (e.g. `169.254.169.254`) that aren't meant to be " \
                "reachable from outside.",
      suggested_fix: "Validate the destination against an allowlist of known-safe hosts " \
                      "before making the request, rather than passing the user-supplied " \
                      "value straight through — and reject internal/link-local IP ranges " \
                      "explicitly if the allowlist is host-based (DNS can still resolve to one)."
    )
  end

  findings
end