openldap crashes when many users log in

[andreika]

when too many users log in to zimbra imap (from thunderbird or web-interface) slapd chashes without errors

Jan 18 13:05:29 z117 slapd[15252]: connection_closing: readying conn=88 sd=43 for close 
Jan 18 13:05:29 z117 slapd[15252]: connection_close: deferring conn=88 sd=43 
Jan 18 13:05:29 z117 slapd[15252]: daemon: activity on 1 descriptor 
Jan 18 13:05:29 z117 slapd[15252]: conn=88 op=2 do_unbind 
Jan 18 13:05:29 z117 slapd[15252]: conn=88 op=2 UNBIND 
Jan 18 13:05:29 z117 slapd[15252]: daemon: activity on:
Jan 18 13:05:29 z117 slapd[15252]: conn=88 op=1 INTERM oid=1.3.6.1.4.1.4203.1.9.1.4 
Jan 18 13:05:29 z117 slapd[15252]: connection_resched: attempting closing conn=88 sd=43 
Jan 18 13:05:29 z117 slapd[15252]:  
Jan 18 13:05:29 z117 slapd[15252]: connection_close: deferring conn=88 sd=43

loglevel 65535
It happens regulary for example, after reebooting the server - everybody is trying to log in at the same time, so I have to start slapd manually. I wrote a script, but it is a workaround.
what should I try/check?

[quanah]

You need to upgrade, this is a known problem in your ZCS release.

[uxbod]

Not to mention a serious security issue; unless you have applied the patch to the version you are currently running.

[andreika]

okay, thanks