From 1b8fd33c3120bfc6e5164b449e2c2fc9c9306fde Mon Sep 17 00:00:00 2001
From: Thomas Leitner <t_leitner@gmx.at>
Date: Sat, 27 Jun 2020 14:47:21 +0200
Subject: [PATCH 1/2] Add option forbidden_inline_options

It is sometimes necessary to restrict the options that can be set
inline, ie. using the {::options ...} extensions.

By default, the template option is now forbidden to avoid possible
security problems. This addresses CVE-2020-14001.
---
 lib/kramdown/options.rb                        | 10 ++++++++++
 lib/kramdown/parser/kramdown/extensions.rb     |  6 ++++++
 test/testcases/block/12_extension/options.text |  2 ++
 3 files changed, 18 insertions(+)

diff --git a/lib/kramdown/options.rb b/lib/kramdown/options.rb
index ea67913..0214e28 100644
--- a/lib/kramdown/options.rb
+++ b/lib/kramdown/options.rb
@@ -589,6 +589,16 @@ module Kramdown
       Used by: HTML converter
     EOF
 
+    define(:forbidden_inline_options, Object, %w[template], <<~EOF) do |val|
+      Defines the options that may not be set using the {::options} extension
+
+      Default: template
+      Used by: HTML converter
+    EOF
+      val.map! {|item| item.kind_of?(String) ? str_to_sym(item) : item }
+      simple_array_validator(val, :forbidden_inline_options)
+    end
+
   end
 
 end
diff --git a/lib/kramdown/parser/kramdown/extensions.rb b/lib/kramdown/parser/kramdown/extensions.rb
index 493dcf7..637d0fa 100644
--- a/lib/kramdown/parser/kramdown/extensions.rb
+++ b/lib/kramdown/parser/kramdown/extensions.rb
@@ -110,6 +110,12 @@ module Kramdown
           opts.select do |k, v|
             k = k.to_sym
             if Kramdown::Options.defined?(k)
+              if @options[:forbidden_inline_options].include?(k) ||
+                  k == :forbidden_inline_options
+                warning("Option #{k} may not be set inline")
+                next false
+              end
+
               begin
                 val = Kramdown::Options.parse(k, v)
                 @options[k] = val
diff --git a/test/testcases/block/12_extension/options.text b/test/testcases/block/12_extension/options.text
index 5991ab7..b63f34b 100644
--- a/test/testcases/block/12_extension/options.text
+++ b/test/testcases/block/12_extension/options.text
@@ -19,3 +19,5 @@ some <span>*para*</span>
 Some text[^ab].
 
 [^ab]: Some text.
+
+{::options template="/etc/passwd" /}
-- 
2.26.2