Original Writeup on seall.dev

We are given a calculator webpage:

Trying the example payload 0+1234 we get:

Trying all digits, we want to try to reconstruct the word flag to read flag.txt. Let’s try payload 0+123456789:

If 7=f, 1=l, 9=a and 5=g we can do 0+7195 to read the flag.

Flag: KCTF{_c0ngR4t5_KNIGHT_f1naLLy_Y0U_g07_tH3_r1gh7_m4tH_}