Canonical has released a new Linux Intel microcode update for Ubuntu that fixes an issue causing Intel Skylake CPUs to hang after a warm reboot.
On November 12th, 2019, new Intel microcodes were released to mitigate a vulnerability discovered*in the*Transactional Synchronization Extensions (TSX) feature*in Intel processors and*a vulnerability in Intel Xeon*processors that could lead to a denial of service attack from a local privileged*user.
"Intel processors using Transactional Synchronization Extensions (TSX) could expose memory contents previously stored in microarchitectural buffers to a malicious process that is executing on the same CPU core. A local attacker could use this to expose sensitive information. "
After the update was released, a regression was discovered that was causing Intel Skylake processors to hang after a warm reboot.
To resolve this issue, Ubuntu has released the new 'intel-microcode*-*3.20191115.1ubuntu0' that reverts the microcodes for Skylake processors so that they no longer freeze.**
To check if Ubuntu has automatically installed this update, you can check by looking for it in the /var/log/dpkg.log with this command:

fgrep "3.20191115.1" /var/log/dpkg.log | grep " installed "

Ubuntu check for microcodes
For users who to wish to install the new update manually, you can download them for your respective version of Ubuntu from the links below:
Alternatively, Ubuntu users can run the Software Updater program to check for and install the latest updates.