Integer overflow in the __vstrfmon_l function in stdlib/strfmon_l.c in the strfmon implementation in the GNU C Library (aka glibc or libc6) before 2.10.1 allows context-dependent attackers to cause a denial of service (application crash) via a crafted format string, as demonstrated by the %99999999999999999999n string, a related issue to CVE-2008-1391.