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6. From Bugs to Breaches: How Small Mistakes Escalate

A tiny bug can cause massive breaches when combined with insecure assumptions.

Example: Mutable Defaults​

# 6. Insecure
def add_item(item, store=[]):
    store.append(item)
    return store

print(add_item("apple"))
print(add_item("banana"))  # Unexpectedly modifies previous call!

Secure Version​

def add_item(item, store=None):
    if store is None:
        store = []
    store.append(item)
    return store

Example: Error Disclosure​

# 6. Insecure
try:
    1 / 0
except Exception as e:
    print("Error:", e)  # Reveals stack details

# 6. Secure
try:
    1 / 0
except ZeroDivisionError:
    print("Cannot divide by zero.")

✅ Lesson: Defensive programming is how you turn bugs into safe failures instead of breaches.