A flaw was found in curl before version 7.51.0 When re-using a connection,
curl was doing case insensitive comparisons of user name and password with
the existing connections. This means that if an unused connection with
proper credentials exists for a protocol that has connection-scoped
credentials, an attacker can cause that connection to be reused if s/he
knows the case-insensitive version of the correct password.

mdeslaur