|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|
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.
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 servers certificate which is sent in the handshake. This is done in two ways:
You can do this by using the cafile and capath options when creating a <B>Net::LDAPSB> object, and by setting the verify option to require.
1. check that the certificate is signed (trusted) by someone that you trust, and that the certificate hasnt been revoked. For instance, the servers 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 servers certificates 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.
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.
<B>Net::LDAPSB> 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 <B>Net::LDAPSB> object using the ciphers option.
Once youve 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.
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.
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 doesnt 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.
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, perls <B>Authen::SASLB> code cannot negotiate this.
Jim Dutton <email@example.com> provided lots of useful feedback on the early drafts.
Chris Ridd <firstname.lastname@example.org>
Please report any bugs, or post any suggestions, to the perl-ldap mailing list <email@example.com>.
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 v5.20.3||NET::LDAP::SECURITY (3)||2015-04-02|