#34654: Post-normalization performed on the Username field leading to the
bypass of
the whitespace stripping
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Reporter: Sim4n6 | Owner: nobody
Type: Bug | Status: new
Component: contrib.auth | Version: 4.1
Severity: Normal | Keywords:
Triage Stage: Unreviewed | Has patch: 0
Needs documentation: 0 | Needs tests: 0
Patch needs improvement: 0 | Easy pickings: 1
UI/UX: 0 |
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**Summary**
In the Django codebase
[L74](https://github.com/django/django/blob/a52bdea5a27ba44b13eda93642231c65c581e083/django/contrib/auth/forms.py#L74),
when "strip" is enabled
[L265](https://github.com/django/django/blob/a52bdea5a27ba44b13eda93642231c65c581e083/django/forms/fields.py#L265),
the username should not contain any trailing or leading whitespace.
However, after stripping those whitespace
[L278..L279](https://github.com/django/django/blob/a52bdea5a27ba44b13eda93642231c65c581e083/django/forms/fields.py#L278..L279),
normalization is performed. That means stripping whitespaces could be
bypassed in the username using similar Unicode characters as "\u2800"
Take the following case:
result = unicodedata.normalize("NFKC",
"\u2800\u2800sim4n6\u2800\u2800".strip())
In case, the stripped string "sim4n6" contains a leading and trailing
whitespace, that would be deleted and work perfectly.
In case, the stripped string "\u2800\u2800sim4n6\u2800\u2800" contains
similar Unicode characters to the whitespace which could be copied for
instance from https://emptycharacter.com.
**Impact**
There is a security concern regarding including spaces in the username,
plus that, the username is attacker-controlled input.
This means the whitespace stripping on the username could be bypassed and
a remote user could use unintended white space.
@Sim4n6
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Ticket URL: <https://code.djangoproject.com/ticket/34654>
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