The wordexp function in GNU C Library (aka glibc) 2.21 does not enforce the WRDE_NOCMD flag, which allows context-dependent attackers to execute arbitrary commands, as demonstrated by input containing "$((`...`))".
https://sourceware.org/ml/libc-alpha/2014-11/msg00519.html
https://sourceware.org/bugzilla/show_bug.cgi?id=17625
https://security.gentoo.org/glsa/201602-02
https://exchange.xforce.ibmcloud.com/vulnerabilities/98852
http://www.ubuntu.com/usn/USN-2432-1
http://www.securityfocus.com/bid/71216
http://www.oracle.com/technetwork/security-advisory/cpuoct2018-4428296.html
http://www.oracle.com/technetwork/security-advisory/cpujan2018-3236628.html
http://www.debian.org/security/2015/dsa-3142
http://secunia.com/advisories/62146
http://secunia.com/advisories/62100
http://seclists.org/oss-sec/2014/q4/730
http://rhn.redhat.com/errata/RHSA-2014-2023.html
http://lists.opensuse.org/opensuse-updates/2015-02/msg00089.html