A previous update marked DigiNotar signed certificates invalid, excluding a certain subset of certificates that were not marked as untrusted. It is now believed that all certificates signed by DigiNotar should be untrusted.
See the upstream advisory for further details (MFSA 2011-35): http://www.mozilla.org/security/announce/2011/mfsa2011-35.html
This issue has been addressed in following products: Red Hat Enterprise Linux 4 Via RHSA-2011:1266 https://rhn.redhat.com/errata/RHSA-2011-1266.html
This issue has been addressed in following products: Red Hat Enterprise Linux 4 Red Hat Enterprise Linux 5 Red Hat Enterprise Linux 6 Via RHSA-2011:1267 https://rhn.redhat.com/errata/RHSA-2011-1267.html
This issue has been addressed in following products: Red Hat Enterprise Linux 6 Red Hat Enterprise Linux 4 Red Hat Enterprise Linux 5 Via RHSA-2011:1268 https://rhn.redhat.com/errata/RHSA-2011-1268.html