xml.dom.minidom should raise exception on invalid input

@terryjreedy

BPO	12129
Nosy	@terryjreedy, @vadmium, @prodo56
Files	xmlNameVerification.py: code to validate xml element/attribute names

^{Note: these values reflect the state of the issue at the time it was migrated and might not reflect the current state.}

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GitHub fields:

assignee = None
closed_at = None
created_at = <Date 2011-05-20.22:02:10.486>
labels = ['expert-XML', 'type-bug']
title = 'Document Object Model API - validation'
updated_at = <Date 2016-12-23.08:39:36.590>
user = 'https://bugs.python.org/KyleKeating'

bugs.python.org fields:

activity = <Date 2016-12-23.08:39:36.590>
actor = 'pdeep5693'
assignee = 'none'
closed = False
closed_date = None
closer = None
components = ['XML']
creation = <Date 2011-05-20.22:02:10.486>
creator = 'Kyle.Keating'
dependencies = []
files = ['31060']
hgrepos = []
issue_num = 12129
keywords = []
message_count = 7.0
messages = ['136402', '137142', '137487', '137488', '193804', '258344', '283873']
nosy_count = 5.0
nosy_names = ['terry.reedy', 'Kyle.Keating', 'martin.panter', 'jocassid', 'pdeep5693']
pr_nums = []
priority = 'normal'
resolution = None
stage = None
status = 'open'
superseder = None
type = 'behavior'
url = 'https://bugs.python.org/issue12129'
versions = ['Python 2.7', 'Python 3.5', 'Python 3.6']

I was doing some tests on using this library and I noticed xml elements and attribute names could be created with mal-formed xml because special characters which can break validation are not cleaned or converted from their literal forms. Only the attribute values are cleaned, but not the names.

For example

import xml.dom


doc.createElement("p\>\</p\>") 
...

will just embed a pair of p tags in the xml result. I thought that the xml spec did not permit <, >, &, \n etc. in the element name or attribute name? Could I get some clarification on this, thanks!

I suspect you are right, but do not know the rules, and have never used the module. There is no particular person maintaining xml.dom.X at present.

Could you please fill in the ... after the import to give a complete minimal example that fails? Someone could then test it on 3.2

This looks to break pretty good... I did confirm this on 3.0, I'm guessing 3.2 is the same.

import sys
import xml.dom

doc = xml.dom.getDOMImplementation().createDocument(None, 'xml', None)
doc.firstChild.appendChild(doc.createElement('element00'))

element01 = doc.createElement('element01')
element01.setAttribute('attribute', "script><![CDATA[alert('script!');]]></script>")
doc.firstChild.appendChild(element01)

element02 = doc.createElement("script><![CDATA[alert('script!');]]></script>")
doc.firstChild.appendChild(element02)

element03 = doc.createElement("new line \n")

element03.setAttribute('attribute-name','new line \n')
doc.firstChild.appendChild(element03)


print (doc.toprettyxml(indent="  "))

>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>
output:

<?xml version="1.0" ?>
<xml>
<element/>
<element01 attribute="script><![CDATA[alert('script!');]]></script
>"/>
<script><![CDATA[alert('script!');]]></script>/>
<new line
attribute-name="new line
"/>
</xml>

oops, the first xml element in the output should read "<element00/>" not "<element/>"

just a typo! don't get confused!

I added the line print(str(doc)) after the call to getDomImplementation and verified that the errors that I'm seeing are coming from the xml.dom.minidom implemenation of xml.dom. Checking minidom.py I did not see any validation on the tagName that gets passed to createElement. http://www.w3.org/TR/xml11/#NT-NameStartChar lists the format of allowed names. Attached is a file containing the functions I was working on. My thinking is that if the tagName is not valid a ValueError should be thrown.

My limited understanding is that xml.dom and minidom are supposed to implement particular interfaces. So do these DOM interfaces specify if this validation should be done? If so, this would be a bug. Or is it just a question of whether Python should do extra validation not specified by the underlying DOM API?

xml minidom.py needs extra validation in setAttributes for certain special characters depending on the attribute name. Attribute values cannot have special characters like <,> and cant be nested as described in the example below

element01 = doc.createElement('element01')
element01.setAttribute('attribute', "script><![CDATA[alert('script!');]]></script>")
doc.firstChild.appendChild(element01)

script shouldn't be allowed as a value for an attribute and I feel it should throw an exception (Value Exception) and as described above <,> shouldn't be allowed as attributes are more like key-value pairs. Could someone tell me if this is right? If it is, then minidom.py needs this extra level of validation for the same

Fixed in 3.16 by GH-155641. createElement(), createAttribute(), setAttribute() and the other methods taking a name now raise InvalidCharacterErr if it is not a valid XML name, as the DOM requires.

Attribute values are not affected: special characters in them are escaped when the document is serialized.

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xml.dom.minidom should raise exception on invalid input #56338

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xml.dom.minidom should raise exception on invalid input #56338

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KyleKeating commented on May 20, 2011

terryjreedy commented on May 28, 2011

KyleKeating commented on Jun 2, 2011

KyleKeating commented on Jun 2, 2011

jocassid commented on Jul 28, 2013

vadmium commented on Jan 16, 2016

prodo56 commented on Dec 23, 2016

serhiy-storchaka commented on Aug 30, 2026

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