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Notebook Security
Mathematica provides users with access to their computer's file system (Files), interprocess communication (MathLink Mathematica Functions), evaluation of data as code (Converting between Expressions and Strings), and the ability to run arbitrary external programs (Calling External Programs). While these features enable Mathematica users to create powerful programs that can perform truly useful tasks, they bring with them the potential for misuse.
The Mathematica notebook front end provides three mechanisms for evaluating code: Shift+Enter evaluations, initialization cells, and dynamic content.
Shift+Enter Evaluations
Because Shift+Enter evaluations require user interaction to start them, Mathematica provides no safeguards against potentially malicious code that is evaluated using this mechanism. Users should ensure that they do not perform Shift+Enter evaluations on code from untrusted sources. When writing their own code, users should take great care to ensure that the code does not have unintended consequences. For example, Mathematica will not provide a warning when the user evaluates a program to delete files from his or her computer.
Initialization Cells
Initialization cells provide users with a convenient way to evaluate startup code needed by a given notebook when the user first evaluates any input in that notebook. Since this code will be automatically evaluated, likely without the user ever seeing the initialization code, Mathematica will display an alert prompt asking the user to confirm his or her intent to run the initialization code. Users should not evaluate initialization code in a notebook that was obtained from an untrusted source unless the code has been determined to be safe.
- Clicking the Yes button will first evaluate all of the initialization cells in the notebook, then evaluate the selected cells.
- Clicking the No button will not evaluate any of the initialization cells, but will still evaluate the selected cells. Note that this may cause errors in the evaluations since they may rely on startup code that has not yet been evaluated.
- Clicking the Cancel button will cause neither the initialization cells nor the selected cells to be evaluated.
Dynamic Content
Mathematica has amazing dynamic interactivity features. Notebooks containing interactive Dynamic content can automatically evaluate code without any additional action by the user, aside from opening the notebook file. Many times this is exactly what the user will want, while other times the user should be alerted before this sort of automatic evaluation takes place.
When the user opens a notebook containing dynamic content, Mathematica will first determine whether the notebook's directory is trusted, untrusted, or neither.
- If the notebook's directory is trusted, the notebook will be allowed to automatically perform dynamic evaluations without alerting the user.
- If the notebook's directory is neither trusted nor untrusted, the behavior will depend on the value of the
option explained as follows.
Mathematica provides some options which can be used to configure which notebooks will alert the user about automatic evaluations and which notebooks will not.
TrustedPath
The value of the 
option is a list of directories that are always trusted by Mathematica. Any notebook file located in any directory in 
is trusted by Mathematica. Mathematica will never display an alert when a trusted notebook is opened, and the notebook can automatically perform dynamic evaluations.
By default, the 
option value contains $InstallationDirectory, $BaseDirectory, and $UserBaseDirectory so that Mathematica installation files and additional installed applications will be able to display dynamic content without alerting the user.
Here are the directories on your computer that are currently trusted by Mathematica:
UntrustedPath
The value of the 
option is a list of directories that are always untrusted by Mathematica. Any notebook file located in any directory in 
is untrusted by Mathematica. Mathematica will always display an alert when an untrusted notebook is opened and attempts to perform dynamic evaluations.
By default, the 
option value contains the user's desktop folder (where web browser downloads are likely to be stored), the user's configuration folder (where email attachments are likely to be stored), and the computer's temporary directory. If the user has configured his or her web browser or email program to save downloaded files in nonstandard locations, then the user is encouraged to add these locations to the 
option value.
Here are the directories on your computer that are currently untrusted by Mathematica:
Nesting
Directories in 
and 
can be nested. A notebook is trusted if the most deeply nested directory containing the notebook is trusted. Consider the following example:
- FrontEnd`FileName[{$HomeDirectory, "Desktop"}, "SomeDownload.nb"] would be untrusted because "Desktop" is untrusted.
- FrontEnd`FileName[{$HomeDirectory, "Desktop", "SafeNotebooks"}, "MyNotebook.nb"] would be trusted because "SafeNotebooks" is trusted.
TrustByDefault
The 
option determines whether Mathematica should display an alert when the user opens notebooks with dynamic content whose containing directories are neither trusted nor untrusted. Below are the possible values for the 
option.
| True | a notebook which is not located in a directory in  is considered to be trusted and will not display an alert when opened |
| False | a notebook which is not located in a directory in  is considered to be untrusted and will display an alert when opened |
| Automatic | a notebook which is not located in any directory in either  or  will display an alert when opened only if the notebook contains unsafe dynamic content (see below) |
The current value of the 
option is: 
Unsafe Dynamic Content
Dynamic content is considered unsafe if it:
- uses File operations
- uses interprocess communication via MathLink Mathematica Functions
- uses data as code by Converting between Expressions and Strings
- uses Namespace Management
- uses Options Management
- uses External Programs
Changing Option Values
, 
, and 
are options in the 
category. They can be changed using the "Preferences..." dialog or the "Option Inspector...".
Any attempt to change the value of the 
, 
, or 
options will cause Mathematica to prompt the user to confirm the change. Mathematica does this as a security precaution so that malicious code cannot change the value of these options without the user's knowledge.
