Prevention of XML injection attacks
from django.http import HttpResponse
from lxml import etree
def parse_xml(request):
xml_data = request.POST['xml_data']
tree = etree.fromstring(xml_data)
# process XML data...
return HttpResponse("XML processed")
The above code is a simple Django view that accepts POST requests containing XML data in the 'xml_data' field. The XML data is parsed using the lxml library's
fromstring
function.
The vulnerability lies in the fact that the XML data is directly parsed without any validation or sanitization. This means that if an attacker sends a malicious XML payload (for example, an XML External Entity (XXE) injection), the server will process it, potentially leading to data exfiltration, Denial of Service (DoS), or remote code execution.
An XXE attack could look like this:
]>
&xxe;
from django.http import HttpResponse
from lxml import etree
from lxml.etree import XMLSyntaxError
def parse_xml(request):
xml_data = request.POST['xml_data']
parser = etree.XMLParser(resolve_entities=False)
try:
tree = etree.fromstring(xml_data, parser)
except XMLSyntaxError:
return HttpResponse("Invalid XML data")
# process XML data...
return HttpResponse("XML processed")
The updated code includes several changes to mitigate the risk of XML External Entity (XXE) injection attacks.
1. Disable External Entity Resolution: The
XMLParser
is now configured with
resolve_entities=False
. This prevents the parser from processing any external entities referenced in the XML data, which is a common vector for XXE attacks.
2. Input Validation: The
etree.fromstring()
function is now wrapped in a try/except block that catches
XMLSyntaxError
exceptions. This exception is raised when the input data is not well-formed XML. By catching this exception, the application can reject invalid XML data before it is processed further.
3. Secure XML Parser: The code continues to use the
lxml
library for parsing XML data. While this library is not specifically designed for handling untrusted input, it does provide several features for mitigating common XML-related vulnerabilities, including the ability to disable external entity processing. If the application needs to process untrusted XML data on a regular basis, it may be worth considering a more secure alternative, such as
defusedxml
.
The other recommendations, such as implementing access controls, regularly updating dependencies, and performing security testing, are not reflected in the code as they pertain to broader application and infrastructure security practices.