Buffer overflow in CHICKEN 4.9.0.x before 4.9.0.2, 4.9.x before 4.9.1, and before 5.0 allows attackers to have unspecified impact via a positive START argument to the "substring-index[-ci] procedures."
https://security.gentoo.org/glsa/201612-54
http://www.securityfocus.com/bid/72011
http://lists.nongnu.org/archive/html/chicken-users/2015-01/msg00048.html
http://lists.nongnu.org/archive/html/chicken-hackers/2014-12/msg00000.html