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Net::LDAP::Security(3)	       User Contributed Perl Documentation	   Net::LDAP::Security(3)

       Net::LDAP::Security - Security issues with LDAP connections


       This document discusses various security issues relating to using LDAP and connecting to
       LDAP servers, notably how to manage these potential vulnerabilities:

       o   do you know that you are connected to the right server

       o   can someone sniff your passwords/userids from the directory connection

       o   can someone sniff other confidential information from the directory connection

       Net::LDAP provides ways to address these vulnerabilities: through the use of LDAPS, or
       LDAPv3 and TLS, and/or the use of SASL. Each of these will be explained below.

   How does an LDAP connection work
       A normal LDAPv2 or LDAPv3 connection works by the client connecting directly to port 389
       (by default), and then issuing various LDAP requests like search, add, etc.

       There is no way to guarantee that an LDAP client is connected to the right LDAP server.
       Hackers could have poisoned your DNS, so 'ldap.example.com' could be made to point to
       'ldap.hacker.com'. Or they could have installed their own server on the correct machine.

       It is in the nature of the LDAP protocol that all information goes between the client and
       the server in 'plain text'. This is a term used by cryptographers to describe unencrypted
       and recoverable data, so even though LDAP can transfer binary values like JPEG
       photographs, audio clips and X.509 certificates, everything is still considered 'plain

       If these vulnerabilities are an issue to, then you should consider the other possibilities
       described below, namely LDAPS, LDAPv3 and TLS, and SASL.

   How does an LDAPS connection work
       LDAPS is an unofficial protocol. It is to LDAP what HTTPS is to HTTP, namely the exact
       same protocol (but in this case LDAPv2 or LDAPv3) running over a secured SSL ("Secure
       Socket Layer") connection to port 636 (by default).

       Not all servers will be configured to listen for LDAPS connections, but if they do, it
       will commonly be on a different port from the normal plain text LDAP port.

       Using LDAPS can potentially solve the vulnerabilities described above, but you should be
       aware that simply "using" SSL is not a magic bullet that automatically makes your system

       First of all, LDAPS can solve the problem of verifying that you are connected to the
       correct server. When the client and server connect, they perform a special SSL
       'handshake', part of which involves the server and client exchanging cryptographic keys,
       which are described using X.509 certificates. If the client wishes to confirm that it is
       connected to the correct server, all it needs to do is verify the server's certificate
       which is sent in the handshake. This is done in two ways:

       1.  check that the certificate is signed (trusted) by someone that you trust, and that the
	   certificate hasn't been revoked. For instance, the server's certificate may have been
	   signed by Verisign (www.verisign.com), and you decide that you want to trust Verisign
	   to sign legitimate certificates.

       2.  check that the least-significant cn RDN in the server's certificate's DN is the fully-
	   qualified hostname of the hostname that you connected to when creating the LDAPS
	   object. For example if the server is <cn=ldap.example.com,ou=My department,o=My
	   company>, then the RDN to check is cn=ldap.example.com.

       You can do this by using the cafile and capath options when creating a Net::LDAPS object,
       and by setting the verify option to 'require'.

       To prevent hackers 'sniffing' passwords and other information on your connection, you also
       have to make sure the encryption algorithm used by the SSL connection is good enough. This
       is also something that gets decided by the SSL handshake - if the client and server cannot
       agree on an acceptable algorithm the connection is not made.

       Net::LDAPS will by default use all the algorithms built into your copy of OpenSSL, except
       for ones considered to use "low" strength encryption, and those using export strength
       encryption. You can override this when you create the Net::LDAPS object using the
       'ciphers' option.

       Once you've made the secure connection, you should also check that the encryption
       algorithm that is actually being used is one that you find acceptable. Broken servers have
       been observed in the field which 'fail over' and give you an unencrypted connection, so
       you ought to check for that.

   How does LDAP and TLS work
       SSL is a good solution to many network security problems, but it is not a standard. The
       IETF corrected some defects in the SSL mechanism and published a standard called RFC 2246
       which describes TLS ("Transport Layer Security"), which is simply a cleaned up and
       standardized version of SSL.

       You can only use TLS with an LDAPv3 server. That is because the standard (RFC 4511) for
       LDAP and TLS requires that the normal LDAP connection (ie., on port 389) can be switched
       on demand from plain text into a TLS connection. The switching mechanism uses a special
       extended LDAP operation, and since these are not legal in LDAPv2, you can only switch to
       TLS on an LDAPv3 connection.

       So the way you use TLS with LDAPv3 is that you create your normal LDAPv3 connection using
       "Net::LDAP::new()", and then you perform the switch using "Net::LDAP::start_tls()". The
       "start_tls()" method takes pretty much the same arguments as "Net::LDAPS::new()", so check
       above for details.

   How does SASL work
       SASL is an authentication framework that can be used by a number of different Internet
       services, including LDAPv3. Because it is only a framework, it doesn't provide any way to
       authenticate by itself; to actually authenticate to a service you need to use a specific
       SASL mechanism. A number of mechanisms are defined, such as CRAM-MD5.

       The use of a mechanism like CRAM-MD5 provides a solution to the password sniffing
       vulnerability, because these mechanisms typically do not require the user to send across a
       secret (eg., a password) in the clear across the network. Instead, authentication is
       carried out in a clever way which avoids this, and so prevents passwords from being

       Net::LDAP supports SASL using the Authen::SASL class. Currently the only Authen::SASL
       subclasses (ie., SASL mechanism) available are CRAM-MD5 and EXTERNAL.

       Some SASL mechanisms provide a general solution to the sniffing of all data on the network
       vulnerability, as they can negotiate confidential (ie., encrypted) network connections.
       Note that this is over and above any SSL or TLS encryption! Unfortunately, perl's
       Authen::SASL code cannot negotiate this.

       Net::LDAP, Net::LDAPS, Authen::SASL

       Jim Dutton <jimd@dutton3.it.siu.edu> provided lots of useful feedback on the early drafts.

       Chris Ridd <chris.ridd@isode.com>

       Please report any bugs, or post any suggestions, to the perl-ldap mailing list

       Copyright (c) 2001-2004 Chris Ridd. All rights reserved. This program is free software;
       you can redistribute it and/or modify it under the same terms as Perl itself.

perl v5.16.3				    2013-06-07			   Net::LDAP::Security(3)
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