The Yahoo! Tumblr app before 3.4.1 for iOS sends cleartext credentials, which allows remote attackers to obtain sensitive information by sniffing the network.
https://itunes.apple.com/us/app/tumblr/id305343404
https://exchange.xforce.ibmcloud.com/vulnerabilities/85823
http://www.theregister.co.uk/2013/07/17/tumblr_ios_snafu_fixed/
http://staff.tumblr.com/post/55648373578/important-security-update-for-iphone-ipad-users