The vfprintf function in stdio-common/vfprintf.c in libc in GNU C Library (aka glibc) 2.14 and other versions does not properly calculate a buffer length, which allows context-dependent attackers to bypass the FORTIFY_SOURCE format-string protection mechanism and cause a denial of service (segmentation fault and crash) via a format string with a large number of format specifiers that triggers "desynchronization within the buffer size handling," a different vulnerability than CVE-2012-3404.