MacDirectory 113
FEATURE
Only a few weeks after the recent release
of macOS High Sierra 10.13.4, Apple has
amended the update by publishing an
additional fix under this version number.
Addressing a new flaw described as
"serious" by the security community, the
supplemental version of 10.13.4 addresses
a problem in Intel CPUs discovered near
the end of April that affects a broad number
of devices, including Windows and Linux
machines. However, unlike the Spectre and
Meltdown flaws that caused much concern
due to their so-called "unpatchable" nature,
there is a way to address this problem.
What's the issue? The bug concerns a
process called "exception handling" which is
one of the most basic and vital functions of
modern processors. When the CPU detects
anomalous conditions such as an instruction
for the CPU that causes a problem or could
yield a potential error, that instruction gets
flagged as an exception. The CPU puts
a pause on the exception, runs the good
instructions waiting in line behind it, and
then looks for a way to handle the exception
when free cycles become available.
However, in this particular case, exceptions
involving specific sets of instructions (such
as a "stack switch"), can fool the CPU into
allowing them to run before identifying their
nature. In other words, it's a way to bypass
one of the most important safeguards to
ensure proper processor operation. An
attacker who develops an exploit to use
this flaw could then potentially escalate their
privileges to be able to run arbitrary code
with full access or to crash the system.
The good news, however, is that an
attacker would need physical access and
a guest login to the machine to be able
to run software capable of exploiting the
flaw. Remote execution, in this case, is
not possible and therefore not a concern.
Despite the rare chance that you might
encounter this problem at all, it remains a
good idea to refresh your version of macOS
to ensure you have the full benefits of all the
most recent security updates for your Mac.
For more information, visit:
www.securemac.com
