Stack-based buffer overflow in the get_matching_model_microcode function in arch/x86/kernel/cpu/microcode/intel_early.c in the Linux kernel before 4.0 allows context-dependent attackers to gain privileges by constructing a crafted microcode header and leveraging root privileges for write access to the initrd.
http://lists.fedoraproject.org/pipermail/package-announce/2015-March/153329.html
http://rhn.redhat.com/errata/RHSA-2015-1534.html
https://bugzilla.redhat.com/show_bug.cgi?id=1204722
https://github.com/torvalds/linux/commit/f84598bd7c851f8b0bf8cd0d7c3be0d73c432ff4