I try to setup LDAPS authentification on Zabbix 2.4 but it's not working. Here is the infos on my configuration :

  • OS : Debian
  • PHP packages installed : libapache2-mod-php5 php-pear php5 php5-cli php5-common php5-curl php5-gd php5-imagick php5-json php5-ldap php5-mysqlnd php5-pgsql php5-readline php5-sasl zabbix-frontend-php

  • This command is working :

ldapsearch -H ldaps://ldaps.mptest.be:636 -D cn=reader,dc=antidot,dc=prv -W -b ou=people,dc=antidot,dc=prv

Same URI, OU, login, password in the Authentification LDAP setup page on zabbix, I have this :

ldap_bind(): Unable to bind to server: Can't contact LDAP server

[authentication.php:120 → CLdapAuthValidator->validate() → CLdap->checkPass() → ldap_bind() in /usr/share/zabbix/include/classes/ldap/CLdap.php:112] LDAP: cannot bind by given Bind DN. Login name or password is incorrect!

Here is the content of /etc/ldap/ldap.conf: TLS_REQCERT allow BASE dc=antidot,dc=prv URI ldaps://ldap.mptest.be TLS_CACERTDIR /etc/ssl/mptest/wildcard_mptest_be.ca

(Authentification without SSL, on port 386 is not possible)

  • What version of Debian? Have you checked connectivity without SSL (be careful with this, change password immediately after if you do)? Tell us also contents of /etc/ldap.conf. – sam_pan_mariusz Aug 24 '15 at 7:31
  • Thanks for your reply, I edit the main post with the ldap config. unfortunately, Ldap on port 386 without SSL is not possible. – Nico_Melotte Aug 24 '15 at 7:57
  • Everything seems to be fine here. Are there any per-process or per-user firewall rules? Have you tested LDAPS connectivity with another, simple PHP script? And have you considered authenticating in httpd (Apache?) and passing REMOTE_USER to application? Zabbix works that way in my workplace (although with Kerberos, not LDAP, as we prefer having SSO). – sam_pan_mariusz Aug 24 '15 at 8:52
  • I did try a test PHP : code<?php $handle = ldap_connect('ldaps://ldaps.mptest.be',636); $bind = ldap_bind($handle, 'cn=reader,dc=antidot,dc=prv', 'reader'); echo "TEST BIND"; if ($bind) { if (ldap_get_option($handle, LDAP_OPT_DIAGNOSTIC_MESSAGE, $extended_error)) { echo "Error Binding to LDAP: $extended_error"; } else { echo "Error Binding to LDAP: No additional information is available."; } } else { echo "not binding"; } ?>code – Nico_Melotte Aug 24 '15 at 8:55
  • And i have a dokuwiki page that is using that LDAPS server but in anoymous – Nico_Melotte Aug 24 '15 at 9:04

This is what works on Ubuntu 14.04. Debian based system should be the same:


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  • Welcome to Server Fault! Whilst this may theoretically answer the question, it would be preferable to include the essential parts of the answer here, and provide the link for reference. – Gerald Schneider Jul 14 '17 at 17:25
  • The tip in the answer is really good, and I think that this was the site that also helped me getting onto the right track. Good input, thank you @jouflux. – hargut Jan 4 '19 at 23:04

I resolved this problem by visiting the Zabbix web interface, then going to Administration -> Authentication -> LDAP and changing the LDAP host parameter from hostname (e.g. ldap.example.com) to its IP address (e.g.,

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PHP's LDAP is, to be frank, pure crap. Some time ago I did also struggle with Zabbix and LDAPS. You can do everything 100% correct, but it will still fail. So, no worries, the issue here is not on your side.

To get that working you have to disable TLS/SSL certificate validation in OpenLDAP. PHP's LDAP uses the OpenLDAP libraries, and therefore /etc/openldap/ldap.conf or ~/.ldaprc are loaded and matter. (This can be seen, using an example PHP LDAP query and running that with strace -e trace=open php example.php). The problem here seems to be located in the area of PHPs usage of the OpenLDAP libraries, some missing/wrong/not implemented calls for successful TLS certificate validation. Fixing that would involve patching PHP.

TLS_REQCERT never should be the parameter needed to get that going. The URL and OU/DC settings in ldap.conf should not be relevant as they are provided from the Zabbix configuration. I strongly suggest to modify that in ~/.ldaprc of your webservers home directory, to not affect any other application using LDAPS.

This solution is not a good one, but still better than falling back to unencrypted LDAP. And just to clarify, I tried it with manually placing CACerts for OpenLDAP, regenerating the cert cache and setting TLS_REQCERT to always. This worked fine using e.g. ldapsearch (uses the same librarie as PHP), but still failed with PHPs LDAP feature. So this attempt will likely be a waste of time. I did not try to place the client certificate and use TLS_KEY/TLS_CERT as indicated in the answer from @jouflux. If that works it would be a better solution.

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