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 XML vulnerabilities.
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 vulnerabilities for e.g. denial of service attacks, to access local files, to generate network connections to other machines, or to or circumvent firewalls. The attacks on XML abuse unfamiliar features like inline DTD (document type definition) with entities.
The following table gives an overview of the known attacks and if 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 ParserError when 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 of defusedxml on PyPI has further information about all known attack vectors with examples and references.
These external packages are recommended for any code that parses untrusted XML data.
defusedxml is a pure Python package with modified subclasses of all stdlib XML parsers that prevent any potentially malicious operation. The package also ships with example exploits and extended documentation on more XML exploits like xpath injection.
defusedexpat provides a modified libexpat and patched replacement
pyexpat extension module with countermeasures against entity expansion DoS attacks. Defusedexpat still allows a sane and configurable amount of entity expansions. The modifications will be merged into future releases of Python.
The workarounds and modifications are not included in patch releases as they break backward compatibility. After all inline DTD and entity expansion are well-defined XML features.
© 2001–2017 Python Software Foundation
Licensed under the PSF License.