Apache-SSL optional client certificate vulnerability

From the Apache-SSL security advisory:

If configured with SSLVerifyClient set to 1 or 3 (client certificates optional) and SSLFakeBasicAuth, Apache-SSL 1.3.28+1.52 and all earlier versions would permit a client to use real basic authentication to forge a client certificate.

All the attacker needed is the "one-line DN" of a valid user, as used by faked basic auth in Apache-SSL, and the fixed password ("password" by default).