On 4/16/2026 11:51 AM, Ken Hornstein via Kerberos wrote:
In the matter of security there is the non answered second part of the
question. How to verify server certificate even when using ldaps? I see
no option to specify CA certificate or demanding server certificate
verification.
FWIW, I personally wouldn't say ldaps is "much more secure" than start_tls,
but fine, it's not something I care to argue about. But my memory is that
at least with OpenLDAP there is a configuration file where you can specify
all of these things. Also since OpenLDAP links against a separate TLS
library you could put server CA certificates in the "usual place" where
the TLS library implementation looks for those things. We use a non-public
PKI infrastructure for our LDAP server and we put those server certificates
in the appropriate place for the operating system and it Just Works.
Using the "usual place" is questionable, as it includes the mass of
Internet CAs. If you trust them to never issue certs for your LDAP
server name, fine. I'm less sanguine about the security of random CAs
(and there have been multiple past incidents of bogus certs being issued).
To control the additional LDAP options, you can either set environment
variables in your krb5kdc process, or set up an ldaprc / ldapconf file.
So either set LDAPTLS_CACERT / LDAPTLS_CACERTDIR env vars, or the
TLS_CACERT / TLS_CACERTDIR options in ldaprc. You can also set TLS_CERT
/ TLS_KEY to use an X.509 client cert for AuthN.
To specify a location for an ldaprc file, set HOME and LDAPRC env vars,
or specify LDAPCONF. You may also want to set LDAPNOINIT. Some options
can't be set in an ldap.conf file.
I wish krb5kdc exposed a mechanism to set arbitrary OpenLDAP options,
but the above should do what you want.
--
Carson
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