mirror of
https://github.com/python/cpython.git
synced 2025-07-12 05:45:15 +00:00
cb99d99277
* Remove the table * Replace warnings with notes Latest releases of Python 3.9-3.15 include expat 2.7.1 which is not vulnerable. expat 2.6.0 was released in February 2024.
94 lines
3.2 KiB
ReStructuredText
94 lines
3.2 KiB
ReStructuredText
.. _xml:
|
|
|
|
XML Processing Modules
|
|
======================
|
|
|
|
.. module:: xml
|
|
:synopsis: Package containing XML processing modules
|
|
|
|
.. sectionauthor:: Christian Heimes <christian@python.org>
|
|
.. sectionauthor:: Georg Brandl <georg@python.org>
|
|
|
|
**Source code:** :source:`Lib/xml/`
|
|
|
|
--------------
|
|
|
|
Python's interfaces for processing XML are grouped in the ``xml`` package.
|
|
|
|
.. note::
|
|
|
|
If you need to parse untrusted or unauthenticated data, see
|
|
:ref:`xml-security`.
|
|
|
|
It is important to note that modules in the :mod:`xml` package require that
|
|
there be at least one SAX-compliant XML parser available. The Expat parser is
|
|
included with Python, so the :mod:`xml.parsers.expat` module will always be
|
|
available.
|
|
|
|
The documentation for the :mod:`xml.dom` and :mod:`xml.sax` packages are the
|
|
definition of the Python bindings for the DOM and SAX interfaces.
|
|
|
|
The XML handling submodules are:
|
|
|
|
* :mod:`xml.etree.ElementTree`: the ElementTree API, a simple and lightweight
|
|
XML processor
|
|
|
|
..
|
|
|
|
* :mod:`xml.dom`: the DOM API definition
|
|
* :mod:`xml.dom.minidom`: a minimal DOM implementation
|
|
* :mod:`xml.dom.pulldom`: support for building partial DOM trees
|
|
|
|
..
|
|
|
|
* :mod:`xml.sax`: SAX2 base classes and convenience functions
|
|
* :mod:`xml.parsers.expat`: the Expat parser binding
|
|
|
|
|
|
.. _xml-security:
|
|
.. _xml-vulnerabilities:
|
|
|
|
XML security
|
|
------------
|
|
|
|
An attacker can abuse XML features to carry out denial of service attacks,
|
|
access local files, generate network connections to other machines, or
|
|
circumvent firewalls.
|
|
|
|
Expat versions lower that 2.6.0 may be vulnerable to "billion laughs",
|
|
"quadratic blowup" and "large tokens". Python may be vulnerable if it uses such
|
|
older versions of Expat as a system-provided library.
|
|
Check :const:`!pyexpat.EXPAT_VERSION`.
|
|
|
|
:mod:`xmlrpc` is **vulnerable** to the "decompression bomb" attack.
|
|
|
|
|
|
billion laughs / exponential entity expansion
|
|
The `Billion Laughs`_ attack -- also known as exponential entity expansion --
|
|
uses multiple levels of nested entities. Each entity refers to another entity
|
|
several times, and the final entity definition contains a small string.
|
|
The exponential expansion results in several gigabytes of text and
|
|
consumes lots of memory and CPU time.
|
|
|
|
quadratic blowup entity expansion
|
|
A quadratic blowup attack is similar to a `Billion Laughs`_ attack; it abuses
|
|
entity expansion, too. Instead of nested entities it repeats one large entity
|
|
with a couple of thousand chars over and over again. The attack isn't as
|
|
efficient as the exponential case but it avoids triggering parser countermeasures
|
|
that forbid deeply nested entities.
|
|
|
|
decompression bomb
|
|
Decompression bombs (aka `ZIP bomb`_) apply to all XML libraries
|
|
that can parse compressed XML streams such as gzipped HTTP streams or
|
|
LZMA-compressed
|
|
files. For an attacker it can reduce the amount of transmitted data by three
|
|
magnitudes or more.
|
|
|
|
large tokens
|
|
Expat needs to re-parse unfinished tokens; without the protection
|
|
introduced in Expat 2.6.0, this can lead to quadratic runtime that can
|
|
be used to cause denial of service in the application parsing XML.
|
|
The issue is known as :cve:`2023-52425`.
|
|
|
|
.. _Billion Laughs: https://en.wikipedia.org/wiki/Billion_laughs
|
|
.. _ZIP bomb: https://en.wikipedia.org/wiki/Zip_bomb
|