After installing the most recent security and Safari updates (7.1.5) on Mavericks, Safari and other applications (those using NSURLConnection/CFURLConnection) no longer recognize any root certificates as valid. The root certificates in the System Roots keychain seem to be fine, as far as Keychain Access is concerned. However, Safari, iTunes, Chrome, etc. fail to validate all root certificates ("This certificate was signed by an unknown authority"). Already tried deleting the /var/db/crls/crlcache.db and /var/db/crls/ocspcache.db to no effect. System time is correct. Any ideas?
Were able to solve the issue myself. For some reason, there were a few root certificates in my login Keychain, which have been revoked and replaced with newer certs in the System Roots keychain. Deleted those certs from my login keychain and everything works fine again.