Source code: Lib/xml/
Python’s interfaces for processing XML are grouped in the
The XML modules are not secure against erroneous or maliciously constructed data. If you need to parse untrusted or unauthenticated data see the XML vulnerabilities and The defusedxml and defusedexpat Packages sections.
It is important to note that modules in the
xml package require that there be at least one SAX-compliant XML parser available. The Expat parser is included with Python, so the
xml.parsers.expat module will always be available.
The XML handling submodules are:
xml.etree.ElementTree: the ElementTree API, a simple and lightweight XML processor
xml.dom: the DOM API definition
xml.dom.minidom: a minimal DOM implementation
xml.dom.pulldom: support for building partial DOM trees
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.
|external entity expansion||Vulnerable||Safe (1)||Safe (2)||Vulnerable||Safe (3)|
xml.etree.ElementTreedoesn’t expand external entities and raises a
ParserErrorwhen an entity occurs.
xml.dom.minidomdoesn’t expand external entities and simply returns the unexpanded entity verbatim.
xmlrpclibdoesn’t expand external entities and omits them.
xml.dom.pulldomretrieve document type definitions from remote or local locations. The feature has similar implications as the external entity expansion issue.
The documentation for defusedxml on PyPI has further information about all known attack vectors with examples and references.
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
pyexpat module that have countermeasures against entity expansion DoS attacks. The
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.
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