Testing for LDAP Injection (OTG-INPVAL-006)

[Up]

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 a user to login with his own credentials or search other users informations inside a corporate structure.

The primary concept on LDAP Injection is that in occurrence of an LDAP query during execution flow, it is possible to fool a vulnerable web application by using LDAP Search Filters metacharacters.

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

A 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 result in:

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

Boolean conditions and group aggregations on an LDAP search filter could be applied by using the following metacharacters: More complete examples on how to build a search filter could be found in related RFC.

A successful exploitation of LDAP Injection could allow the tester to:


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

Example 1. Search Filters
Let's suppose we have 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 'John' value is replaced with a '*', by sending the request:

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

the filter will look like:

searchfilter="(cn=*)"

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

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

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

Example 2. Login
If a web application uses a vulnerable login page with LDAP query for user credentials, it is possible to bypass the check for user/password presence 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 three.