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Net::LDAP::Security(3pUser Contributed Perl DocumentatNet::LDAP::Security(3pm)



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

SYNOPSIS
         none

DESCRIPTION
       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
       text'.

       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 "secure".

       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 2830) 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
       sniffed.

       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.

SEE ALSO
       Net::LDAP, Net::LDAPS, Authen::SASL

ACKNOWLEDGEMENTS
       Jim Dutton <jimdATdutton3.edu> provided lots of useful feedback
       on the early drafts.

AUTHOR
       Chris Ridd <chris.riddATisode.com>

       Please report any bugs, or post any suggestions, to the perl-ldap
       mailing list <perl-ldapATperl.org>.

COPYRIGHT
       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 v5.10.0                      2008-04-21          Net::LDAP::Security(3pm)