A vulnerability was found in kexec, allowing the attacker to bypass the security mechanism of securelevel/secureboot combination.

When the kernel was booted with UEFI Secure Boot enabled, securelevel is set. If kexec (either through crash or admin action) is then used to load the same kernel, after reboot securelevel is disabled. In this state, the system is missing the protections provided by securelevel, for example kexec may be used to load an unsigned kernel via the legacy system call kexecload. In the securelevel patchset, the state of UEFI Secure Boot is queried in the EFI stub, and sets a bootparams flag to indicate the state of UEFI Secure Boot. This flag is then used in setuparch() to determine the correct state of securelevel. If the kernel is not booted via the EFI stub, securelevel is not set even if UEFI Secure Boot is enabled.

Patch can be found in product bug:

https://bugzilla.redhat.com/showbug.cgi?id=1243998#c3

Upstream patch:

https://github.com/mjg59/linux/commit/4b2b64d5a6ebc84214755ebccd599baef7c1b798

CVE assignment:

http://seclists.org/oss-sec/2015/q4/85