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   1  =head1 NAME
   2  
   3  Net::LDAP::Security - Security issues with LDAP connections
   4  
   5  =head1 SYNOPSIS
   6  
   7    none
   8  
   9  =head1 DESCRIPTION
  10  
  11  This document discusses various security issues relating to using LDAP
  12  and connecting to LDAP servers, notably how to manage these potential
  13  vulnerabilities:
  14  
  15  =over 4
  16  
  17  =item *
  18  
  19  do you know that you are connected to the right server
  20  
  21  =item *
  22  
  23  can someone sniff your passwords/userids from the directory connection
  24  
  25  =item *
  26  
  27  can someone sniff other confidential information from the directory
  28  connection
  29  
  30  =back
  31  
  32  B<Net::LDAP> provides ways to address these vulnerabilities: through the
  33  use of LDAPS, or LDAPv3 and TLS, and/or the use of SASL. Each of these
  34  will be explained below.
  35  
  36  =head2 How does an LDAP connection work
  37  
  38  A normal LDAPv2 or LDAPv3 connection works by the client connecting
  39  directly to port 389 (by default), and then issuing various LDAP
  40  requests like search, add, etc.
  41  
  42  There is no way to guarantee that an LDAP client is connected to the
  43  right LDAP server. Hackers could have poisoned your DNS, so
  44  'ldap.example.com' could be made to point to 'ldap.hacker.com'. Or
  45  they could have installed their own server on the correct machine.
  46  
  47  It is in the nature of the LDAP protocol that all information goes
  48  between the client and the server in 'plain text'. This is a term used
  49  by cryptographers to describe unencrypted and recoverable data, so
  50  even though LDAP can transfer binary values like JPEG photographs,
  51  audio clips and X.509 certificates, everything is still considered
  52  'plain text'.
  53  
  54  If these vulnerabilities are an issue to, then you should consider the
  55  other possibilities described below, namely LDAPS, LDAPv3 and TLS, and
  56  SASL.
  57  
  58  =head2 How does an LDAPS connection work
  59  
  60  LDAPS is an unofficial protocol. It is to LDAP what HTTPS is to HTTP,
  61  namely the exact same protocol (but in this case LDAPv2 or LDAPv3)
  62  running over a I<secured> SSL ("Secure Socket Layer") connection to
  63  port 636 (by default).
  64  
  65  Not all servers will be configured to listen for LDAPS connections,
  66  but if they do, it will commonly be on a different port from the normal
  67  plain text LDAP port.
  68  
  69  Using LDAPS can I<potentially> solve the vulnerabilities described
  70  above, but you should be aware that simply "using" SSL is not a magic
  71  bullet that automatically makes your system "secure".
  72  
  73  First of all, LDAPS can solve the problem of verifying that you are
  74  connected to the correct server. When the client and server connect,
  75  they perform a special SSL 'handshake', part of which involves the
  76  server and client exchanging cryptographic keys, which are described
  77  using X.509 certificates. If the client wishes to confirm that it is
  78  connected to the correct server, all it needs to do is verify the
  79  server's certificate which is sent in the handshake. This is done in
  80  two ways:
  81  
  82  =over 4
  83  
  84  =item 1
  85  
  86  check that the certificate is signed (trusted) by someone that you
  87  trust, and that the certificate hasn't been revoked. For instance, the
  88  server's certificate may have been signed by Verisign
  89  (www.verisign.com), and you decide that you want to trust Verisign to
  90  sign legitimate certificates.
  91  
  92  =item 2
  93  
  94  check that the least-significant cn RDN in the server's certificate's
  95  DN is the fully-qualified hostname of the hostname that you connected
  96  to when creating the LDAPS object. For example if the server is
  97  E<lt>cn=ldap.example.com,ou=My department,o=My companyE<gt>, then the
  98  RDN to check is cn=ldap.example.com.
  99  
 100  =back
 101  
 102  You can do this by using the cafile and capath options when creating a
 103  B<Net::LDAPS> object, I<and> by setting the verify option to 'require'.
 104  
 105  To prevent hackers 'sniffing' passwords and other information on your
 106  connection, you also have to make sure the encryption algorithm used
 107  by the SSL connection is good enough. This is also something that gets
 108  decided by the SSL handshake - if the client and server cannot agree
 109  on an acceptable algorithm the connection is not made.
 110  
 111  B<Net::LDAPS> will by default use all the algorithms built into your copy
 112  of OpenSSL, except for ones considered to use "low" strength
 113  encryption, and those using export strength encryption. You can
 114  override this when you create the B<Net::LDAPS> object using the
 115  'ciphers' option.
 116  
 117  Once you've made the secure connection, you should also check that the
 118  encryption algorithm that is actually being used is one that you find
 119  acceptable. Broken servers have been observed in the field which 'fail
 120  over' and give you an unencrypted connection, so you ought to check
 121  for that.
 122  
 123  =head2 How does LDAP and TLS work
 124  
 125  SSL is a good solution to many network security problems, but it is
 126  not a standard. The IETF corrected some defects in the SSL mechanism
 127  and published a standard called RFC 2246 which describes TLS
 128  ("Transport Layer Security"), which is simply a cleaned up and
 129  standardized version of SSL.
 130  
 131  You can only use TLS with an LDAPv3 server. That is because the
 132  standard (RFC 2830) for LDAP and TLS requires that the I<normal> LDAP
 133  connection (ie., on port 389) can be switched on demand from plain text
 134  into a TLS connection. The switching mechanism uses a special extended
 135  LDAP operation, and since these are not legal in LDAPv2, you can only
 136  switch to TLS on an LDAPv3 connection.
 137  
 138  So the way you use TLS with LDAPv3 is that you create your normal
 139  LDAPv3 connection using C<Net::LDAP::new()>, and then you perform the
 140  switch using C<Net::LDAP::start_tls()>. The C<start_tls()> method takes
 141  pretty much the same arguments as C<Net::LDAPS::new()>, so check above for
 142  details.
 143  
 144  =head2 How does SASL work
 145  
 146  SASL is an authentication framework that can be used by a number of
 147  different Internet services, including LDAPv3. Because it is only a
 148  framework, it doesn't provide any way to authenticate by itself; to
 149  actually authenticate to a service you need to use a specific SASL
 150  I<mechanism>. A number of mechanisms are defined, such as CRAM-MD5.
 151  
 152  The use of a mechanism like CRAM-MD5 provides a solution to the
 153  password sniffing vulnerability, because these mechanisms typically do
 154  not require the user to send across a secret (eg., a password) in the
 155  clear across the network. Instead, authentication is carried out in a
 156  clever way which avoids this, and so prevents passwords from being
 157  sniffed.
 158  
 159  B<Net::LDAP> supports SASL using the B<Authen::SASL> class. Currently the
 160  only B<Authen::SASL> subclasses (ie., SASL mechanism) available are
 161  CRAM-MD5 and EXTERNAL.
 162  
 163  Some SASL mechanisms provide a general solution to the sniffing of all
 164  data on the network vulnerability, as they can negotiate confidential
 165  (ie., encrypted) network connections. Note that this is over and above
 166  any SSL or TLS encryption! Unfortunately, perl's B<Authen::SASL> code
 167  cannot negotiate this.
 168  
 169  =head1 SEE ALSO
 170  
 171  L<Net::LDAP>,
 172  L<Net::LDAPS>,
 173  L<Authen::SASL>
 174  
 175  =head1 ACKNOWLEDGEMENTS
 176  
 177  Jim Dutton E<lt>jimd@dutton3.it.siu.eduE<gt> provided lots of useful feedback
 178  on the early drafts.
 179  
 180  =head1 AUTHOR
 181  
 182  Chris Ridd E<lt>chris.ridd@isode.comE<gt>
 183  
 184  Please report any bugs, or post any suggestions, to the perl-ldap mailing list
 185  E<lt>perl-ldap@perl.orgE<gt>.
 186  
 187  =head1 COPYRIGHT
 188  
 189  Copyright (c) 2001-2004 Chris Ridd. All rights reserved. This program is
 190  free software; you can redistribute it and/or modify it under the same
 191  terms as Perl itself.
 192  
 193  =cut