After upgrading to Mojave lpass-cli fails to execute properly?
This issue appears to be with lpass itself, after upgrading to Mojave. The issue was reported in various forms on the LastPass Github project page for lastpass-cli. Specifically this issue: Segfaults on macOS Mojave Beta #427.

The solution is pretty straightforward. Simply upgrading lastpass-cli via brew like so:

$ brew upgrade lastpass-cli


Resulting in this version being installed which fixes the malloc issue mentioned.

$ brew info lastpass-cli
lastpass-cli: stable 1.3.3 (bottled), HEAD
LastPass command-line interface tool
https://github.com/lastpass/lastpass-cli
/usr/local/Cellar/lastpass-cli/1.3.3 (10 files, 216.6KB) *
  Poured from bottle on 2019-04-15 at 15:15:05
From: https://github.com/Homebrew/homebrew-core/blob/master/Formula/lastpass-cli.rb
==&gt; Dependencies
Build: asciidoc ✘, cmake ✘, docbook-xsl ✔, pkg-config ✔
Required: curl ✔, openssl ✔, pinentry ✔
==&gt; Options
--HEAD
    Install HEAD version
==&gt; Caveats
Bash completion has been installed to:
  /usr/local/etc/bash_completion.d

zsh completions have been installed to:
  /usr/local/share/zsh/site-functions
==&gt; Analytics
install: 2,555 (30 days), 5,077 (90 days), 18,589 (365 days)
install_on_request: 2,378 (30 days), 4,832 (90 days), 17,108 (365 days)
build_error: 0 (30 days)


Version details from CLI:

$ lpass --version
LastPass CLI v1.3.3.GIT