At the risk of appearing to be obtuse...I tried both versions of the "do" and got the same results. In each case, the variable was populated but no code was executed. In a test stack with one field and one button, I entered ";set the backcolor of btn 1 to blue;put ". In the button script I tried both versions of your example (substituting "fld 1" for "user input".) I also tried it without the semicolons and extra "put " at the end.

In each case the variable x contained "set the backcolor of btn 1 to blue" and the button did not change color.

I am quite sure you are right, but could you provide an example where the embedded command would actually execute?

On 3/30/18 7:06 PM, Mark Waddingham via use-livecode wrote:
The user input was indirected through a variable in the safe version - not made 
part of the do string... That's the critical difference.

The unsafe version allows user input to change the do'd code, the safe version 
only changes the content of a variable the do string uses.

Warmest Regards,

Mark.

Sent from my iPhone

On 30 Mar 2018, at 19:24, J. Landman Gay via use-livecode 
<use-livecode@lists.runrev.com> wrote:

Well yes, but as Bob mentioned, wouldn't a variable do the same thing?

  put ";delete hard drive;put " into x
  do x

vs:

  do "put " && quote & ";delete hard drive;put " & quote && "into x"

This actually came up way back in MetaCard where it was pointed out that the engine was about as secure as it 
gets as long as you validate all user input when using "do" or (I think) "value". In the 
first example above, input needs to be examined before the "do" command is issued. So I think 
there's a line or two missing in there somewhere. ;)


On 3/30/18 12:15 PM, Mark Waddingham via use-livecode wrote:
Think about the string that can be constructed in the quoted version - user input could 
be "; ...;put " where ... is any code you would like...
Sent from my iPhone
On 30 Mar 2018, at 18:09, J. Landman Gay via use-livecode 
<use-livecode@lists.runrev.com> wrote:

These look the same to me. Both versions place content into a variable. Is the 
difference because of how the engine evaluates the input somehow?

--
Jacqueline Landman Gay | jac...@hyperactivesw.com
HyperActive Software | http://www.hyperactivesw.com
On March 30, 2018 11:04:54 AM Mark Waddingham via use-livecode 
<use-livecode@lists.runrev.com> wrote:

Using do safely is the same as making database queries safe, or URL requests.

You 'just' need to make sure that any input from outside is sanitized to ensure 
that it doesn't change the meaning of the expression you are 'doing'.

For example, don't interpolate strings directly in the script using quotes, use 
a local var instead:

put user input into tVar1
do "put tVar1 into x" -- safe

Rather than

do "put " && quote & user input & quote && "into x" -- not safe

Warmest Regards,

Mark.

Sent from my iPhone

On 30 Mar 2018, at 16:43, Tom Glod via use-livecode 
<use-livecode@lists.runrev.com> wrote:

Dear Geniuses

Sometimes.... late at night just before falling asleep I think about the
dangers of the do command.  Is it possible to inject code into this
mechanism through malware?

I do not have enough understanding of operating systems and their processes
...and the livecode engine....to be able to know if its a reasonable
question or not.

Thanks for any input on this.
_______________________________________________


--
Jacqueline Landman Gay         |     jac...@hyperactivesw.com
HyperActive Software           |     http://www.hyperactivesw.com

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--
Jacqueline Landman Gay         |     jac...@hyperactivesw.com
HyperActive Software           |     http://www.hyperactivesw.com

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