Ask HN: Why don't banks render numbers as PNGs instead of using HTML?

2 points by 4RealFreedom 1 year ago | 25 comments

I've been thinking about scammers lately and thought about rendering numbers as a png in browsers instead of displaying them as HMTL for banks. This would ensure scammers can't just go in and edit the html on the fly potentially saving some people from this kind of attack.

I played around with libvips and can easily create a png with any text.

vips text x.png "1,234,567" --width 100 --align centre --dpi 340

Any thoughts on why this shouldn't be done?

solardev 1 year ago |

I don't understand your threat model:

> This would ensure scammers can't just go in and edit the html on the fly

How would the scammers "edit the HTML on the fly" of a bank's website that they don't control...?

If they can control it somehow (either via a hack, local malware, browser extension, or just hand-editing the site on the victim's computer)... well, they can just as easily replace your PNG with one of their own, or just replace it with regular HTML numbers.

If someone can control the bank website, it's game over. It's not a matter of graphics vs text?

4RealFreedom 1 year ago | |

They ask a person to login to their bank account with screen sharing. They then take control of the mouse and edit the HTML on the fly making it look like they transferred a large amount to the bank account. Now they ask the person to wire money back or they will lose their job.

solardev 1 year ago | | |

If they already control your browser, they don't have to edit the HTML and fake anything. They can just transfer money to themselves from your account...

If they wanted to edit the HTML for some reason, it's trivial to just use their own image or replace the <img> with their own text.

The prevention for this isn't to render texts as image, but not to screen share your computer with random people online, much less hand mouse control over to them while you're logged in to your bank. If it's some elderly person doing this or the such, you should really teach them better or they'll get scammed from much less esoteric threats :(

theandrewbailey 1 year ago |

1. This would break accessibility requirements.

2. Scammers can fake PNGs just like HTML.

4RealFreedom 1 year ago | |

I'll give you accessibility. I tried changing images in the browser on the fly and it just hides the image. That's probably because the browser would need to make a new GET request.

solardev 1 year ago | | |

That's probably a content security policy or CSS thing. Just tried it on a site (not HN, because of content security) and it worked fine.

akshardave 1 year ago |

This is a legit good idea and I don't think there's any reason not to do this. I had a similar idea to instead render the balance amount inside a canvas to make it difficult for a scammer to change it. Could also add event listeners to the canvas so when the canvas element or its nearby/parent elements get removed or changed, the page could automatically logout and show an alert message warning about a possible scam. For accessibility, aria-* tags could still be added and there could be ways to allow copying the balance amount too.

al_borland 1 year ago |

I often login to my bank to copy an account number when I need it. I don’t like to rely on typing it correctly. This change would kill that. Sure, I could use OCR on the image, but that isn’t 100% perfect, like a text copy is.

They will also likely just come up with a small tweak on the scam if there is a change like this. I’ve watched some of the videos where they pull up a command prompt and run a script where the user is entering the amount to transfer into the CLI. When they type the amount the scammer slips in an extra 0 before the user presses enter. If someone is going to fall for entering their info into a strange black box with text, they will fall for literally anything. The scammer could simply delete the image on the page so the balance doesn’t show and say there is a bug… or delete the image and replace it with text, even if it looks off, the type of person being targeted won’t catch it.

tonetegeatinst 1 year ago |

Probably accessibility reasons. Even ancient browsers or obscure browsers support text. Their is a non zero chance a browser wouldn't support the image format, or the image might not scale across different screen sizes. Also iirc their was some vulnerability that used a image format so that's also a issue to think about.

Finally, text makes web scraping/parsing much easier, and even ignoring that text is smaller than any image format.

4RealFreedom 1 year ago | |

Couldn't alt-text be used to address accessibility?

Web scrapping shouldn't be a requirement of personal banking websites. Am I missing something here?

stop50 1 year ago |

Then how do access people with vision problems the website? Afaik only the banks in Germany use FINTS for banking

4RealFreedom 1 year ago | |

Had to look up FINTS. You are right about accessibility.

Ekaros 1 year ago |

If you are already dealing with scammers. Well they will find the ways around it and put energy in it.

And for the rest it will just many times annoy them for no gain.

nextos 1 year ago |

My bank used to do this. They also forced you to type things for certain operations using a screen keyboard where key labels were shuffled.