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Security-focused static analysis for Elixir & the Phoenix framework
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Files
lib/sobelow/config/csp.ex
defmodule Sobelow.Config.CSP do
@moduledoc """
# Missing Content-Security-Policy
Content-Security-Policy is an HTTP header that helps mitigate
a number of attacks, including Cross-Site Scripting.
Read more about CSP here:
https://developer.mozilla.org/en-US/docs/Web/HTTP/CSP
Missing Content-Security-Policy is flagged by `sobelow` when
a pipeline implements the `:put_secure_browser_headers` plug,
but does not provide a Content-Security-Policy header in the
custom headers map.
Documentation on the `put_secure_browser_headers` plug function
can be found here:
https://hexdocs.pm/phoenix/Phoenix.Controller.html#put_secure_browser_headers/2
Content-Security-Policy checks can be ignored with the following command:
$ mix sobelow -i Config.CSP
"""
alias Sobelow.Config
use Sobelow.Finding
@finding_type "Config.CSP: Missing Content-Security-Policy"
def run(router, _) do
meta_file = Parse.ast(router) |> Parse.get_meta_funs()
finding = Finding.init(@finding_type, Utils.normalize_path(router))
Config.get_pipelines(router)
|> Enum.map(&check_vuln_pipeline(&1, meta_file))
|> Enum.each(&maybe_add_finding(&1, finding))
end
def check_vuln_pipeline({:pipeline, _, [_name, [do: block]]} = pipeline, meta_file) do
{vuln?, conf, plug} =
Config.get_plug_list(block)
|> Enum.find(&is_header_plug?/1)
|> missing_csp_status(meta_file)
{vuln?, conf, plug, pipeline}
end
defp is_header_plug?({:plug, _, [:put_secure_browser_headers]}), do: true
defp is_header_plug?({:plug, _, [:put_secure_browser_headers, _]}), do: true
defp is_header_plug?(_), do: false
defp missing_csp_status({_, _, [:put_secure_browser_headers]} = plug, _),
do: {true, :high, plug}
defp missing_csp_status({_, _, [:put_secure_browser_headers, {:%{}, _, opts}]} = plug, _) do
{!include_csp?(opts), :high, plug}
end
defp missing_csp_status({_, _, [:put_secure_browser_headers, {:@, _, opts}]} = plug, meta_file) do
[{attr, _, nil} | _] = opts
has_csp? =
Enum.find_value(meta_file.module_attrs, fn mod_attr ->
case mod_attr do
{^attr, _, [{:%{}, _, definition}]} -> definition
_ -> false
end
end)
|> include_csp?()
{!has_csp?, :high, plug}
end
defp missing_csp_status({_, _, [:put_secure_browser_headers, _]} = plug, _),
do: {true, :low, plug}
defp missing_csp_status(plug, _), do: {false, :high, plug}
defp include_csp?(nil), do: false
defp include_csp?(headers) do
Enum.any?(headers, fn
{key, _} when is_binary(key) ->
String.downcase(key) == "content-security-policy"
_ ->
false
end)
end
defp maybe_add_finding(
{true, confidence, plug, {:pipeline, _, [pipeline_name, _]} = pipeline},
finding
) do
%{
finding
| vuln_source: :put_secure_browser_headers,
vuln_line_no: Parse.get_fun_line(plug),
fun_source: pipeline,
fun_name: pipeline_name,
confidence: confidence
}
|> add_finding()
end
defp maybe_add_finding(_, _), do: nil
defp add_finding(%Finding{} = finding) do
finding = Finding.fetch_fingerprint(finding)
file_header = "File: #{finding.filename}"
pipeline_header = "Pipeline: #{finding.fun_name}"
line_header = "Line: #{finding.vuln_line_no}"
case Sobelow.format() do
"json" ->
json_finding = [
type: finding.type,
file: finding.filename,
pipeline: finding.fun_name,
line: finding.vuln_line_no
]
Sobelow.log_finding(json_finding, finding)
"txt" ->
Sobelow.log_finding(finding)
Print.print_custom_finding_metadata(
finding,
[file_header, pipeline_header, line_header]
)
"compact" ->
Print.log_compact_finding(finding)
_ ->
Sobelow.log_finding(finding)
end
end
end