Comment 5 for bug 1852581

I can confirm that disabling Secure Boot does indeed allow the system to boot normally.

$ uname -srvp
Linux 5.3.0-23-generic #25~18.04.1-Ubuntu SMP Tue Nov 12 10:58:57 UTC 2019 x86_64

$ sudo od -An -t u1 /sys/firmware/efi/vars/SecureBoot-8be4df61-93ca-11d2-aa0d-00e098032b8c/data
   0

$ inxi -v 1
System: Host: HOSTNAME Kernel: 5.3.0-23-generic x86_64 bits: 64 Desktop: MATE 1.20.1
           Distro: Ubuntu 18.04.3 LTS
CPU: Dual core Intel Core i5-4200U (-MT-MCP-) speed/max: 1044/2600 MHz
Graphics: Card-1: Intel Haswell-ULT Integrated Graphics Controller
           Card-2: NVIDIA GK208M [GeForce GT 740M]
           Display Server: x11 (X.Org 1.20.4 ) drivers: modesetting (unloaded: fbdev,vesa)
           Resolution: 1366x768@60.00hz
           OpenGL: renderer: Mesa DRI Intel Haswell Mobile version: 4.5 Mesa 19.2.1
Drives: HDD Total Size: 250.1GB (5.5% used)
Info: Processes: 208 Uptime: 2 min Memory: 487.5/7845.5MB Client: Shell (bash) inxi: 2.3.56

As an additional data point, the output of dmesg when dropped to the initramfs prompt reveals:
...
Run /init as init process
Lockdown: systemd-udevd: Loading of unsigned module is restricted; see man kernel_lockdown.7
...

FWIW, 5.0.0-36-generic (i.e. the newest 18.04 HWE, non-edge kernel) is *not* affected by this issue and boots normally with Secure Boot enabled.