Big Blacklist

Description Link to heading

That’s a big blacklist for a pyjail challenge, don’t you think? Author: NoobMaster

nc challs.n00bzunit3d.xyz 8412

Solving Link to heading

Once connected on the server, we can find the code of the PyJail.

blacklist = ["/","0","1","2","3","4","5","6","7","8","9","setattr","compile","globals", \
    "os","import","_","breakpoint","exit","lambda","eval","exec","read","print", \
    "open","'","=",'"',"x","builtins","clear"]
print("="*25)
print(open(__file__).read())
print("="*25)
print("Welcome to the jail!")
print("="*25)

for i in range(2):
    x = input('Enter command: ')
    for c in blacklist:
            if c in x:
                print("Blacklisted word found! Exiting!")
                exit(0)
    exec(x)

We can see that there is a big blacklist array. But in the same time we are able to send two different input in the same code execution.

Then first, we will clear all the array by using a special font that is recognize by the system. This will bypass the blacklist because it is not in the array. Once the array is empty, we can call any python functions.

Enter command: 𝔟𝔩𝔞𝔠𝔨𝔩𝔦𝔰𝔱.𝔠𝔩𝔢𝔞𝔯()
Enter command: print(open('flag.txt').read())

Result Link to heading

n00bz{blacklist.pop()_ftw!_7a5d2f8b}