chain.c in back-ldap in OpenLDAP 2.4.x before 2.4.24, when a master-slave configuration with a chain overlay and ppolicy_forward_updates (aka authentication-failure forwarding) is used, allows remote authenticated users to bypass external-program authentication by sending an invalid password to a slave server.
https://bugzilla.redhat.com/show_bug.cgi?id=680466
https://bugzilla.novell.com/show_bug.cgi?id=674985
http://www.vupen.com/english/advisories/2011/0665
http://www.ubuntu.com/usn/USN-1100-1
http://www.redhat.com/support/errata/RHSA-2011-0347.html
http://www.redhat.com/support/errata/RHSA-2011-0346.html
http://www.openldap.org/lists/openldap-technical/201004/msg00247.html
http://www.openldap.org/lists/openldap-announce/201102/msg00000.html
http://www.openldap.org/its/index.cgi/Software%20Bugs?id=6607
http://www.mandriva.com/security/advisories?name=MDVSA-2011:056
http://www.mandriva.com/security/advisories?name=MDVSA-2011:055
http://securitytracker.com/id?1025188
http://security.gentoo.org/glsa/glsa-201406-36.xml
http://secunia.com/advisories/43718
http://secunia.com/advisories/43708
http://secunia.com/advisories/43331
http://openwall.com/lists/oss-security/2011/02/25/13
http://openwall.com/lists/oss-security/2011/02/24/12
http://kb.juniper.net/InfoCenter/index?page=content&id=JSA10735
http://kb.juniper.net/InfoCenter/index?page=content&id=JSA10705