Hi,

exactly the same here:

[ 793.696338] VBoxClient[2457]: segfault at 968 ip 00007f36e10fae0d sp 00007ffd98ecf250 error 4 in libX11.so.6.3.0[7f36e10dd000+8b000]
[ 793.696350] Code: 56 49 89 f6 41 55 49 89 d5 41 54 49 89 cc 55 48 89 fd 53 4c 89 c3 48 83 ec 38 64 48 8b 04 25 28 00 00 00 48 89 44 24 28 31 c0 <48> 8b 87 68 09 00 00 48 85 c0 74 02 ff 10 ba 08 00 00 00 be 62 00

[...]

ii virtualbox-guest-dkms 6.1.4-dfsg-1 all x86 virtualization solution - guest addition module source for dkms
ii virtualbox-guest-utils 6.1.4-dfsg-1 amd64 x86 virtualization solution - non-X11 guest utilities
ii virtualbox-guest-x11 6.1.4-dfsg-1 amd64 x86 virtualization solution - X11 guest utilities

$ uname -a
Linux kali-008 5.4.0-kali4-amd64 #1 SMP Debian 5.4.19-1kali1 (2020-02-17) x86_64 GNU/Linux
... running as a VB guest on Ubuntu 18.04 host.