mutated × unstructured — blows up live on input you didn't expect

Integration Crash on Unexpected Input

Trusting an external payload's shape, then mutating local state from it.

01the recipe

In the wild

compound ofImpure FunctionsCWE-1108 Global RelianceLack of Input ValidationCWE-20 Input ValidationcompoundCWE-248 Uncaught Exception CWE-754 Unchecked Condition

example.py

# SMELL: trust a third party's shape; mutate local state from it.
# (impure-functions / external read x lack-of-input-validation)
resp = requests.get(url).json()      # third party, shape not guaranteed
user.age = resp["profile"]["age"]    # KeyError the day they rename a field
                                     # -- first seen live, in the demo

# RIGHT: validate at the boundary; fail with a clear, handled error.
data = UserSchema.parse(resp)        # parse, don't trust
user.age = data.profile.age

The crash isn't in your logic -- it's the contract you never enforced at the edge. It appears the first time the integration sends a shape you didn't anticipate.

// observed

unexpected: KeyError 'profile' when their API changes
validated: a clear ValidationError you handle, not a 500

02weakness catalog

Mapped weaknesses (CWE)

On its own, this defect is catalogued by MITRE as one or more of these weaknesses. The exploitable vulnerability usually appears only when it chains or combines with another.