Thursday, April 05, 2012

Lovely week connecting LDAP client on RHEL to Windows AD over TLS/SSL

A client contacted us to enable SSL connection in Request Tracker's integration with LDAP. It was epic battle.

We had

First of all, Windows Server 2008 R2 with Active Directory, but it has an "add-on" installed that hardens security. On other side RHEL 6, Apache running RT with mod_perl and serving it via HTTPS.


Everything works just fine as long as you don't use secure connection to LDAP. If start_tls is enabled or you try to connect via ldaps:// then AD drops connection after first packet and client throws "connection reset by peer" error.


From perl modules we moved down to `openssl s_client` command and got the same results. AD admins failed to provide any helpful information, so we captured ldp.exe session with wireshark. No surprise microsoft client worked just fine. Comparison of handshake packets ldp and s_client send showed that MS's LDAP client announce EDHCE group of cipher suits, openssl doesn't. Openssl project implemented this family of ciphers based on elliptic curves, but for whatever reason RHEL ships openssl without them.


So we compiled the latest openssl and installed it in its own location. Compiled Net::SSLeay against new openssl and installed it into custom location. Client was using Apache with mod_perl, but we had to switch to FastCGI. This is required as apache uses openssl library for HTTPS and we don't want perl and apache to load different versions of the library into the same process. mod_fcgid is not available in RHEL, but you can get it from EPEL repository. Simple patch to RT to put special library paths into @INC.

Hope it would help somebody.

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