The ares_init:randomize_key function in c-ares, on platforms other than Windows, uses a weak facility for producing a random number sequence (Unix rand), which makes it easier for remote attackers to spoof DNS responses by guessing certain values.
https://exchange.xforce.ibmcloud.com/vulnerabilities/34980
http://www.securityfocus.com/bid/24386
http://cool.haxx.se/cvs.cgi/curl/ares/CHANGES?rev=HEAD&content-type=text/vnd.viewcvs-markup