A flaw was found in curl. This flaw lies in the --ssl-reqd option or related settings in libcurl. Users specify this flag to upgrade to TLS when communicating with either IMAP, POP3 or a FTP server. An attacker controlling such servers could return a crafted response which could lead to curl client continue its operation without TLS encryption leading to data being transmitted in clear text over the network. The highest threat from this vulnerability is to data confidentiality.