diff options
Diffstat (limited to 'Doc/library/xml.rst')
| -rw-r--r-- | Doc/library/xml.rst | 76 |
1 files changed, 12 insertions, 64 deletions
diff --git a/Doc/library/xml.rst b/Doc/library/xml.rst index d4959953989..28465219a1a 100644 --- a/Doc/library/xml.rst +++ b/Doc/library/xml.rst @@ -15,12 +15,10 @@ XML Processing Modules Python's interfaces for processing XML are grouped in the ``xml`` package. -.. warning:: +.. note:: - 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:`defusedxml-package` sections. + 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 @@ -47,46 +45,22 @@ The XML handling submodules are: * :mod:`xml.parsers.expat`: the Expat parser binding +.. _xml-security: .. _xml-vulnerabilities: -XML vulnerabilities -------------------- +XML security +------------ -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** (1) **Vulnerable** (1) **Vulnerable** (1) **Vulnerable** (1) **Vulnerable** (1) -quadratic blowup **Vulnerable** (1) **Vulnerable** (1) **Vulnerable** (1) **Vulnerable** (1) **Vulnerable** (1) -external entity expansion Safe (5) Safe (2) Safe (3) Safe (5) Safe (4) -`DTD`_ retrieval Safe (5) Safe Safe Safe (5) Safe -decompression bomb Safe Safe Safe Safe **Vulnerable** -large tokens **Vulnerable** (6) **Vulnerable** (6) **Vulnerable** (6) **Vulnerable** (6) **Vulnerable** (6) -========================= ================== ================== ================== ================== ================== - -1. Expat 2.4.1 and newer is not vulnerable to the "billion laughs" and - "quadratic blowup" vulnerabilities. Items still listed as vulnerable due to - potential reliance on system-provided libraries. Check - :const:`!pyexpat.EXPAT_VERSION`. -2. :mod:`xml.etree.ElementTree` doesn't expand external entities and raises a - :exc:`~xml.etree.ElementTree.ParseError` when an entity occurs. -3. :mod:`xml.dom.minidom` doesn't expand external entities and simply returns - the unexpanded entity verbatim. -4. :mod:`xmlrpc.client` doesn't expand external entities and omits them. -5. Since Python 3.7.1, external general entities are no longer processed by - default. -6. Expat 2.6.0 and newer is not vulnerable to denial of service - through quadratic runtime caused by parsing large tokens. - Items still listed as vulnerable due to - potential reliance on system-provided libraries. Check - :const:`!pyexpat.EXPAT_VERSION`. +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 @@ -103,16 +77,6 @@ quadratic blowup entity expansion 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 @@ -126,21 +90,5 @@ large tokens be used to cause denial of service in the application parsing XML. The issue is known as :cve:`2023-52425`. -The documentation for :pypi:`defusedxml` on PyPI has further information about -all known attack vectors with examples and references. - -.. _defusedxml-package: - -The :mod:`!defusedxml` Package ------------------------------- - -:pypi:`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. - - .. _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 |