Multiple buffer overflows in Cyrus Sieve / libSieve 2.1.2 and earlier allow remote attackers to execute arbitrary code via (1) a long header name, (2) a long IMAP flag, or (3) a script that generates a large number of errors that overflow the resulting error string.
https://exchange.xforce.ibmcloud.com/vulnerabilities/10780
https://exchange.xforce.ibmcloud.com/vulnerabilities/10779
https://exchange.xforce.ibmcloud.com/vulnerabilities/10743
http://www.securityfocus.com/bid/6300