Raise HTTPStatus::BadRequest for requests with invalid/duplicate content-length headers

Addresses CVE-2023-40225.

Fixes #119

Author: jeremyevans

lib/webrick/httprequest.rb

@@ -479,6 +479,14 @@ def read_header(socket)
         end
       end
       @header = HTTPUtils::parse_header(@raw_header.join)
+
+      if (content_length = @header['content-length']) && content_length.length != 0
+        if content_length.length > 1
+          raise HTTPStatus::BadRequest, "multiple content-length request headers"
+        elsif !/\A\d+\z/.match?(content_length[0])
+          raise HTTPStatus::BadRequest, "invalid content-length request header"
+        end
+      end
     end
 
     def parse_uri(str, scheme="http")

test/webrick/test_httprequest.rb

@@ -81,6 +81,31 @@ def test_request_uri_too_large
     }
   end
 
+  def test_invalid_content_length_header
+    ['', ' ', ' +1', ' -1', ' a'].each do |cl|
+      msg = <<-_end_of_message_
+        GET / HTTP/1.1
+        Content-Length:#{cl}
+      _end_of_message_
+      req = WEBrick::HTTPRequest.new(WEBrick::Config::HTTP)
+      assert_raise(WEBrick::HTTPStatus::BadRequest){
+        req.parse(StringIO.new(msg.gsub(/^ {8}/, "")))
+      }
+    end
+  end
+
+  def test_duplicate_content_length_header
+    msg = <<-_end_of_message_
+      GET / HTTP/1.1
+      Content-Length: 1
+      Content-Length: 2
+    _end_of_message_
+    req = WEBrick::HTTPRequest.new(WEBrick::Config::HTTP)
+    assert_raise(WEBrick::HTTPStatus::BadRequest){
+      req.parse(StringIO.new(msg.gsub(/^ {6}/, "")))
+    }
+  end
+
   def test_parse_headers
     msg = <<-_end_of_message_
       GET /path HTTP/1.1