Exploring the Upper() Method in Python: Uncovering Vulnerabilities

Analyzing Character Length Changes with the upper() Method

Hello Everyone, I’d like to share an intriguing discovery I made during a recent CTF (Capture The Flag) challenge centered around the Python upper() method.

Source Code:

@app.route('/login',methods=['GET','POST'])
def login():
    if request.method == 'GET':
        return render_template('login.html')
    elif request.method == 'POST':
        if len(request.values["username"]) >= 40:
            return render_template_string("Username is too long!")
        elif len(request.values["username"].upper()) <= 50:
            return render_template_string("Username is too short!")
        else:
            return flag

Our Goal is to get the flag here but we need …

ctf ctf-writeup python web