Can you solve this?
Additional text appeared when I've launched the instance. All I have is the arithmetic question:
n1 > n1 + n2 OR n2 > n1 + n2
What two positive numbers can make this possible:
We do no have the source code, so, let's try to understand the running application by inserting some data. This is shown in Figure 1:
Figure 1: Analyzing the application
Here, we can see, that entering a very large integers gives us the negative number. So, here we are dealing with Integer overflow. In this case, if we enter the value bigger than INT_MAX the application wil change the first byte (which is actually says if the number is positive or negative) to 1 that will make the number negative.
So, if we google, INT_MAX is equal to 2147483647 (it can depend on architecture, but it worked for me). Then, we can solve the given quest:
2147483647 + 1 will be equal to some negative integer which is less that the initial value. And the same is to the 1.
So, the exploit will look like it is presented below:
2147483647 1
The result is shown in Figure 2:
Figure 2: Solving the task
Here is the flag we received:
picoCTF{Tw0_Sum_Integer_Bu773R_0v3rfl0w_fe14e9e9}
The task wasn't really difficult, but required knowledge and running application analysis.