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I manage a wsgi application that accepts JSON data via POST from potentially untrusted sources. Normally it is treated as a text blob and never parsed, but there is a value in the expected input th...
#1: Initial revision
by
ajv
·
2021-10-19T00:32:16Z (about 3 years ago)
Is it dangerous to use json.loads on untrusted data?
I manage a wsgi application that accepts JSON data via POST from potentially untrusted sources. Normally it is treated as a text blob and never parsed, but there is a value in the expected input that I would like to log.
The obvious way to do it looks like this (where `payload` is the untrusted input):
```py
try:
data = json.loads(payload)
except json.JSONDecodeError as ex:
logging.warning("bad payload: %s", ex)
else:
value = data.get('something', 'ERR_MISSING')
logging.debug("something: %.30s", value)
```
This feels like it *should* be safe, which automatically makes me wonder if it is not. Broken json is handled, and the contents of `data` are not passed to anything other than the logger. But I am uncertain if it's safe to run json.loads on untrusted input, and I'm not sure that all possible json values are safe to stringify for logging.
What am I missing, if anything?