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python3.8.1

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xml.rst

xml.rst 5.92 KB

.. _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.

.. warning::

The XML modules are not secure against erroneous or maliciously
 constructed data. If you need to parse untrusted or
 unauthenticated data see the :ref:`xml-vulnerabilities` and
 :ref:`defused-packages` sections.

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-vulnerabilities:

XML vulnerabilities
-------------------

The XML processing modules are not secure against maliciously constructed data.
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.

The following table gives an overview of the known attacks and whether
the various modules are vulnerable to them.

========================= ============== =============== ============== ============== ==============
kind sax etree minidom pulldom xmlrpc
========================= ============== =============== ============== ============== ==============
billion laughs **Vulnerable** **Vulnerable** **Vulnerable** **Vulnerable** **Vulnerable**
quadratic blowup **Vulnerable** **Vulnerable** **Vulnerable** **Vulnerable** **Vulnerable**
external entity expansion Safe (4) Safe (1) Safe (2) Safe (4) Safe (3)
`DTD`_ retrieval Safe (4) Safe Safe Safe (4) Safe
decompression bomb Safe Safe Safe Safe **Vulnerable**
========================= ============== =============== ============== ============== ==============

1. :mod:`xml.etree.ElementTree` doesn't expand external entities and raises a
 :exc:`ParserError` when an entity occurs.
2. :mod:`xml.dom.minidom` doesn't expand external entities and simply returns
 the unexpanded entity verbatim.
3. :mod:`xmlrpclib` doesn't expand external entities and omits them.
4. Since Python 3.7.1, external general entities are no longer processed by
 default.

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.

external entity expansion
 Entity declarations can contain more than just text for replacement. They can
 also point to external resources or local files. The XML
 parser accesses the resource and embeds the content into the XML document.

`DTD`_ retrieval
 Some XML libraries like Python's :mod:`xml.dom.pulldom` retrieve document type
 definitions from remote or local locations. The feature has similar
 implications as the external entity expansion issue.

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.

The documentation for `defusedxml`_ on PyPI has further information about
all known attack vectors with examples and references.

.. _defused-packages:

The :mod:`defusedxml` and :mod:`defusedexpat` Packages
------------------------------------------------------

`defusedxml`_ is a pure Python package with modified subclasses of all stdlib
XML parsers that prevent any potentially malicious operation. Use of this
package is recommended for any server code that parses untrusted XML data. The
package also ships with example exploits and extended documentation on more
XML exploits such as XPath injection.

`defusedexpat`_ provides a modified libexpat and a patched
:mod:`pyexpat` module that have countermeasures against entity expansion
DoS attacks. The :mod:`defusedexpat` module still allows a sane and configurable amount of entity
expansions. The modifications may be included in some future release of Python,
but will not be included in any bugfix releases of
Python because they break backward compatibility.

.. _defusedxml: https://pypi.org/project/defusedxml/
.. _defusedexpat: https://pypi.org/project/defusedexpat/
.. _Billion Laughs: https://en.wikipedia.org/wiki/Billion_laughs
.. _ZIP bomb: https://en.wikipedia.org/wiki/Zip_bomb
.. _DTD: https://en.wikipedia.org/wiki/Document_type_definition

Copy Edit Raw Blame History

zhangweibo authored 2021年11月16日 09:46 +08:00 . git init

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.

Warning

The XML modules are not secure against erroneous or maliciously constructed data. If you need to parse untrusted or unauthenticated data see the :ref:`xml-vulnerabilities` and :ref:`defused-packages` sections.

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 vulnerabilities

The XML processing modules are not secure against maliciously constructed data. 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.

The following table gives an overview of the known attacks and whether the various modules are vulnerable to them.

kind	sax	etree	minidom	pulldom	xmlrpc
billion laughs	Vulnerable	Vulnerable	Vulnerable	Vulnerable	Vulnerable
quadratic blowup	Vulnerable	Vulnerable	Vulnerable	Vulnerable	Vulnerable
external entity expansion	Safe (4)	Safe (1)	Safe (2)	Safe (4)	Safe (3)
:mod:`xml.etree.ElementTree` doesn't expand external entities and raises a :exc:`ParserError` when an entity occurs. :mod:`xml.dom.minidom` doesn't expand external entities and simply returns the unexpanded entity verbatim. :mod:`xmlrpclib` doesn't expand external entities and omits them. Since Python 3.7.1, external general entities are no longer processed by default. billion laughs / exponential entity expansion The 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. external entity expansion Entity declarations can contain more than just text for replacement. They can also point to external resources or local files. The XML parser accesses the resource and embeds the content into the XML document. :mod:`xml.dom.pulldom` retrieve document type definitions from remote or local locations. The feature has similar implications as the external entity expansion issue. decompression bomb Decompression bombs (aka defusedxml on PyPI has further information about all known attack vectors with examples and references. The :mod:`defusedxml` and :mod:`defusedexpat` Packages defusedexpat provides a modified libexpat and a patched :mod:`pyexpat` module that have countermeasures against entity expansion DoS attacks. The :mod:`defusedexpat` module still allows a sane and configurable amount of entity expansions. The modifications may be included in some future release of Python, but will not be included in any bugfix releases of Python because they break backward compatibility. Loading... Go Report Report success We will send you the feedback within 2 working days through the letter! Please fill in the reason for the report carefully. Provide as detailed a description as possible. Type Please select a report type Reason Cancel Send 误判申诉此处可能存在不合适展示的内容,页面不予展示。您可通过相关编辑功能自查并修改。如您确认内容无涉及不当用语 / 纯广告导流 / 暴力 / 低俗色情 / 侵权 / 盗版 / 虚假 / 无价值内容或违法国家有关法律法规的内容,可点击提交进行申诉,我们将尽快为您处理。取消提交 About No description No labels /python_sourcecode/python3.8.1/blob/master/Doc/library/xml.rst unknown license unknown open source license Code of conduct 0 Stars 1 Watching 0 Forks Cancel Releases No release Contributors All Language(Optional) Python 57.8% C 40.2% C++ 0.7% HTML 0.4% M4 0.3% Other 0.6% Activities can not load any more Edit About Homepage 马建仓 AI 助手尝试更多代码解读代码找茬代码优化 1 https://gitee.com/python_sourcecode/python3.8.1.git git@gitee.com:python_sourcecode/python3.8.1.git python_sourcecode python3.8.1 python3.8.1 master ©OSCHINA. All rights reserved Git Resources Learning Git CopyCat Downloads Gitee Stars Featured Projects Blog Nonprofit Gitee Go OpenAPI MCP Server Help Center Self-services Updates About Us Join us Terms of use Feedback Partners Exchange Exchange 微信服务号 WeChat client#oschina.cn Enterprise:400-606-0201 Pro: 赖经理 13058176526 开放原子开源基金会 OpenAtom Foundation Cooperative code hosting platform 违法和不良信息举报中心违法和不良信息举报中心京ICP备2025119063号京公网安备11011502039387号京公网安备11011502039387号简体 / 繁體 / English Going to Help Center Search Git 命令在线学习如何在 Gitee 导入 GitHub 仓库 Git 仓库基础操作企业版和社区版功能对比 SSH 公钥设置如何处理代码冲突仓库体积过大,如何减小? 如何找回被删除的仓库数据 Gitee 产品配额说明 GitHub仓库快速导入Gitee及同步更新什么是 Release(发行版) 将 PHP 项目自动发布到 packagist.org Comment Repository Report Back to the top Login prompt This operation requires login to the code cloud account. Please log in before operating. Go to login No account. Register AltStyle によって変換されたページ (->オリジナル) / アドレス: モード:

source-code-analysis/python3.8.1

XML Processing Modules

XML vulnerabilities

The :mod:`defusedxml` and :mod:`defusedexpat` Packages

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