5 ms·

JavaScript timers can be bypassed with “Infinity”

• zodiakzz 5y ago
  "Hack"? Cute. Is this guy's first day at programming?
• dragonwriter 5y ago
  Its not “bypassing” if you have to write the code used to setup the timer to do it. I suppose it implies the existence of a class of potential problems if an application (1) accepts user input for timer delays, (2) requires a certain minimum delay, (3) only checks that the entered amount is >= the minimum without considering overflow behavior. But, since this behavior is well-documented (the MDN page on setTimeout covers it), it doesn't seem like any kind of notable discovery.
  • exevp 5y ago
    Also the example of bypassing this is rather contrived: 1) bypassing some timer in an API service requires the API to accept the string „Infinity“ and convert it to the JavaScript value Infinity - which is highly unlikely. Instead, the value would just fail the numeric validation. 2) bypassing some timer in client-side code by injecting Infinity seems overly complex - if you alter client-side code you might aswell just remove the validation instead of abusing edge cases of the language runtime.
    • dragonwriter 5y ago
      > bypassing some timer in an API service requires the API to accept the string „Infinity“ and convert it to the JavaScript value Infinity Yeah, a more realistic bypass would be entering “3000000000”, which would trigger the same behavior.
    • goldenkey 5y ago
      JSON.parse converts 1.0e+1024 to Infinity just fine. ;-)
    • code4money 5y ago
      Will bypass a few validations if server accepts as param from client: Number(Infinity) -> Infinity Infinity < 5000 -> will return false even though Infinity is acting as a 0 here
      • exevp 5y ago
        This is probably a good opportunity to have a heated discussion over parseInt() vs Number() since parseInt('Infinity') yields NaN. I know people prefer Number() for reasons but in this case it reveals the weakness of using basically a typecast with implicit language semantics for interpreting string inputs.
        • goldenkey 5y ago
          parseFloat('Infinity'), JSON.parse('1e1024'), or parseFloat('1e1024') work just fine ;-)
• whoomp12342 5y ago
  this is no different than passing 0 right? I fail to see the significance, other than the fact that infinity doesn't work the way you think it would.
• himinlomax 5y ago
  Am I missing something or is this as dumb as it looks? How's that different from using 0?
  • CryoLogic 5y ago
    If a NodeJS application accepts a value from the client application, but validates against an early call (e.g. min 25 mins from now) the Infinity value can bypass that validation. Because it's a relatively unknown side effect, most validations probably wouldn't check for Infinity. Plus although Infinity pops off the timer at 0 seconds, a validation based on millisecond math would fail because Infinity > 25 minutes in milliseconds.