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Remove reference to the base64 encoding.

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Antoine Pitrou 2011-12-05 01:22:03 +01:00
commit 9b1ec97867
1 changed files with 5 additions and 22 deletions
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Doc/howto/unicode.rst
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@ -552,7 +552,6 @@ should only be used on systems where undecodable file names can be present,
i.e. Unix systems. i.e. Unix systems.
Tips for Writing Unicode-aware Programs Tips for Writing Unicode-aware Programs
--------------------------------------- ---------------------------------------
@ -572,28 +571,12 @@ you do e.g. ``str + bytes``, a :exc:`TypeError` is raised for this expression.
When using data coming from a web browser or some other untrusted source, a When using data coming from a web browser or some other untrusted source, a
common technique is to check for illegal characters in a string before using the common technique is to check for illegal characters in a string before using the
string in a generated command line or storing it in a database. If you're doing string in a generated command line or storing it in a database. If you're doing
this, be careful to check the string once it's in the form that will be used or this, be careful to check the decoded string, not the encoded bytes data;
stored; it's possible for encodings to be used to disguise characters. This is some encodings may have interesting properties, such as not being bijective
especially true if the input data also specifies the encoding; many encodings or not being fully ASCII-compatible. This is especially true if the input
leave the commonly checked-for characters alone, but Python includes some data also specifies the encoding, since the attacker can then choose a
encodings such as ``'base64'`` that modify every single character. clever way to hide malicious text in the encoded bytestream.
For example, let's say you have a content management system that takes a Unicode
filename, and you want to disallow paths with a '/' character. You might write
this code::
def read_file(filename, encoding):
if '/' in filename:
raise ValueError("'/' not allowed in filenames")
unicode_name = filename.decode(encoding)
with open(unicode_name, 'r') as f:
# ... return contents of file ...
However, if an attacker could specify the ``'base64'`` encoding, they could pass
``'L2V0Yy9wYXNzd2Q='``, which is the base-64 encoded form of the string
``'/etc/passwd'``, to read a system file. The above code looks for ``'/'``
characters in the encoded form and misses the dangerous character in the
resulting decoded form.
References References
---------- ----------