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Difference between revisions of "Testing for LDAP Injection (OTG-INPVAL-006)"

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==  Brief Summary ==
 
==  Brief Summary ==
LDAP is an acronym for Lightweight Directory Access Protocol. LDAP is a protocol to store information about users, hosts, and many other objects.
+
LDAP is an acronym for Lightweight Directory Access Protocol. LDAP is a protocol to store information about users, hosts, and many other objects. [[LDAP injection]] is a server side attack, which could allow sensitive information about users and hosts represented in an LDAP structure to be disclosed, modified, or inserted. This is done by manipulating input parameters afterwards passed to internal search, add, and modify functions.
[[LDAP injection]] is a server side attack, which could allow sensitive information about users and hosts represented in an LDAP structure to be disclosed, modified, or inserted.<br>
+
 
This is done by manipulating input parameters afterwards passed to internal search, add, and modify functions.
 
  
 
== Description of the Issue  ==  
 
== Description of the Issue  ==  
  
 
A web application could use LDAP in order to let users authenticate or search other users' information
 
A web application could use LDAP in order to let users authenticate or search other users' information
inside a corporate structure.
+
inside a corporate structure. The goal of LDAP injection attacks is to inject LDAP search filters metacharacters in a query which will be executed by the application.
 
 
The goal of LDAP injection attacks is to inject LDAP search filters metacharacters in a query which will be executed by the application.
 
  
 
[[http://www.ietf.org/rfc/rfc2254.txt Rfc2254]]
 
[[http://www.ietf.org/rfc/rfc2254.txt Rfc2254]]
 
defines a grammar on how to build a search filter on LDAPv3 and
 
defines a grammar on how to build a search filter on LDAPv3 and
 
extends [[http://www.ietf.org/rfc/rfc1960.txt Rfc1960]] (LDAPv2).
 
extends [[http://www.ietf.org/rfc/rfc1960.txt Rfc1960]] (LDAPv2).
 +
  
 
An LDAP search filter is constructed in  Polish notation,  
 
An LDAP search filter is constructed in  Polish notation,  
 
also known as [[http://en.wikipedia.org/wiki/Polish_notation prefix notation]].
 
also known as [[http://en.wikipedia.org/wiki/Polish_notation prefix notation]].
 +
  
 
This means that a pseudo code condition on a search filter like this:
 
This means that a pseudo code condition on a search filter like this:
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  find("(&(cn=John)(userPassword=mypass))")
 
  find("(&(cn=John)(userPassword=mypass))")
 +
  
 
Boolean conditions and group aggregations on an  
 
Boolean conditions and group aggregations on an  
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|-
 
|-
 
|}
 
|}
 +
 +
 
More complete examples on how to build a search filter can be
 
More complete examples on how to build a search filter can be
 
found in the related RFC.
 
found in the related RFC.
 +
  
 
A successful exploitation of an LDAP injection vulnerability could allow the tester to:
 
A successful exploitation of an LDAP injection vulnerability could allow the tester to:
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* Gather unauthorized informations
 
* Gather unauthorized informations
 
* Add or modify Objects inside LDAP tree structure.
 
* Add or modify Objects inside LDAP tree structure.
 +
  
 
== Black Box testing and example ==
 
== Black Box testing and example ==
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which matches every object with a 'cn' attribute equals to anything.
 
which matches every object with a 'cn' attribute equals to anything.
 +
  
 
If the application is vulnerable to LDAP injection, it will display some or all of the users' attributes, depending on the application's execution flow and the permissions of the LDAP connected user.
 
If the application is vulnerable to LDAP injection, it will display some or all of the users' attributes, depending on the application's execution flow and the permissions of the LDAP connected user.
 +
  
 
A tester could use a trial-and-error approach, by inserting in the parameter
 
A tester could use a trial-and-error approach, by inserting in the parameter
 
'(', '|', '&', '*' and the other characters, in order to check  
 
'(', '|', '&', '*' and the other characters, in order to check  
 
the application for errors.
 
the application for errors.
 +
  
 
=== Example 2. Login ===
 
=== Example 2. Login ===
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If a web application uses LDAP to check user credentials during the login process and it is vulnerable to LDAP injection, it is possible to bypass the authentication check by injecting an always true LDAP query (in a similar way to SQL
 
If a web application uses LDAP to check user credentials during the login process and it is vulnerable to LDAP injection, it is possible to bypass the authentication check by injecting an always true LDAP query (in a similar way to SQL
 
and XPATH injection ).
 
and XPATH injection ).
 +
  
 
Let's suppose a web application uses a filter to match LDAP user/password pair.
 
Let's suppose a web application uses a filter to match LDAP user/password pair.
  
 
searchlogin= "(&(uid="+user+")(userPassword={MD5}"+base64(pack("H*",md5(pass)))+"))";
 
searchlogin= "(&(uid="+user+")(userPassword={MD5}"+base64(pack("H*",md5(pass)))+"))";
 +
  
 
By using the following values:
 
By using the following values:
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  searchlogin="(&(uid=*)(uid=*))(|(uid=*)(userPassword={MD5}X03MO1qnZdYdgyfeuILPmQ==))";
 
  searchlogin="(&(uid=*)(uid=*))(|(uid=*)(userPassword={MD5}X03MO1qnZdYdgyfeuILPmQ==))";
  
which is correct and always true.  
+
which is correct and always true. This way, the tester will gain logged-in status as the first user in LDAP tree.
This way, the tester will gain logged-in status as the first user in LDAP tree.
+
 
  
 
== References ==
 
== References ==
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Bruce Greenblatt: "LDAP Overview" - http://www.directory-applications.com/ldap3_files/frame.htm<br>
 
Bruce Greenblatt: "LDAP Overview" - http://www.directory-applications.com/ldap3_files/frame.htm<br>
 
IBM paper: "Understanding LDAP" - http://www.redbooks.ibm.com/redbooks/SG244986.html <br>
 
IBM paper: "Understanding LDAP" - http://www.redbooks.ibm.com/redbooks/SG244986.html <br>
<br>
+
 
 +
 
 
'''Tools'''<br>
 
'''Tools'''<br>
Softerra LDAP Browser - http://www.ldapadministrator.com/ <br>
+
Softerra LDAP Browser - http://www.ldapadministrator.com/
 
 
  
 
<nowiki>RFC 1960</nowiki>: "A String Representation of LDAP Search Filters" - http://www.ietf.org/rfc/rfc1960.txt<br>
 
<nowiki>RFC 1960</nowiki>: "A String Representation of LDAP Search Filters" - http://www.ietf.org/rfc/rfc1960.txt<br>
 
 
]]
 

Revision as of 03:47, 19 May 2014

This article is part of the new OWASP Testing Guide v4.
Back to the OWASP Testing Guide v4 ToC: https://www.owasp.org/index.php/OWASP_Testing_Guide_v4_Table_of_Contents Back to the OWASP Testing Guide Project: https://www.owasp.org/index.php/OWASP_Testing_Project

Brief Summary

LDAP is an acronym for Lightweight Directory Access Protocol. LDAP is a protocol to store information about users, hosts, and many other objects. LDAP injection is a server side attack, which could allow sensitive information about users and hosts represented in an LDAP structure to be disclosed, modified, or inserted. This is done by manipulating input parameters afterwards passed to internal search, add, and modify functions.


Description of the Issue

A web application could use LDAP in order to let users authenticate or search other users' information inside a corporate structure. The goal of LDAP injection attacks is to inject LDAP search filters metacharacters in a query which will be executed by the application.

[Rfc2254] defines a grammar on how to build a search filter on LDAPv3 and extends [Rfc1960] (LDAPv2).


An LDAP search filter is constructed in Polish notation, also known as [prefix notation].


This means that a pseudo code condition on a search filter like this:

find("cn=John & userPassword=mypass")

will be represented as:

find("(&(cn=John)(userPassword=mypass))")


Boolean conditions and group aggregations on an LDAP search filter could be applied by using the following metacharacters:

Metachar Meaning
& Boolean AND
| Boolean OR
 ! Boolean NOT
= Equals
~= Approx
>= Greater than
<= Less than
* Any character
() Grouping parenthesis


More complete examples on how to build a search filter can be found in the related RFC.


A successful exploitation of an LDAP injection vulnerability could allow the tester to:

  • Access unauthorized content
  • Evade application restrictions
  • Gather unauthorized informations
  • Add or modify Objects inside LDAP tree structure.


Black Box testing and example

Example 1. Search Filters

Let's suppose we have a web application using a search filter like the following one:

searchfilter="(cn="+user+")"

which is instantiated by an HTTP request like this:

http://www.example.com/ldapsearch?user=John

If the value 'John' is replaced with a '*', by sending the request:

http://www.example.com/ldapsearch?user=*

the filter will look like:

searchfilter="(cn=*)"

which matches every object with a 'cn' attribute equals to anything.


If the application is vulnerable to LDAP injection, it will display some or all of the users' attributes, depending on the application's execution flow and the permissions of the LDAP connected user.


A tester could use a trial-and-error approach, by inserting in the parameter '(', '|', '&', '*' and the other characters, in order to check the application for errors.


Example 2. Login

If a web application uses LDAP to check user credentials during the login process and it is vulnerable to LDAP injection, it is possible to bypass the authentication check by injecting an always true LDAP query (in a similar way to SQL and XPATH injection ).


Let's suppose a web application uses a filter to match LDAP user/password pair.

searchlogin= "(&(uid="+user+")(userPassword={MD5}"+base64(pack("H*",md5(pass)))+"))";


By using the following values:

user=*)(uid=*))(|(uid=*
 pass=password

the search filter will results in:

searchlogin="(&(uid=*)(uid=*))(|(uid=*)(userPassword={MD5}X03MO1qnZdYdgyfeuILPmQ==))";

which is correct and always true. This way, the tester will gain logged-in status as the first user in LDAP tree.


References

Whitepapers
Sacha Faust: "LDAP Injection: Are Your Applications Vulnerable?" - http://www.networkdls.com/articles/ldapinjection.pdf
Bruce Greenblatt: "LDAP Overview" - http://www.directory-applications.com/ldap3_files/frame.htm
IBM paper: "Understanding LDAP" - http://www.redbooks.ibm.com/redbooks/SG244986.html


Tools
Softerra LDAP Browser - http://www.ldapadministrator.com/

RFC 1960: "A String Representation of LDAP Search Filters" - http://www.ietf.org/rfc/rfc1960.txt