rbash in Bash before 4.4-beta2 did not prevent the shell user from modifying BASH_CMDS, thus allowing the user to execute any command with the permissions of the shell.
{
"binaries": [
{
"binary_name": "bash",
"binary_version": "4.3-7ubuntu1.8+esm1"
},
{
"binary_name": "bash-builtins",
"binary_version": "4.3-7ubuntu1.8+esm1"
},
{
"binary_name": "bash-static",
"binary_version": "4.3-7ubuntu1.8+esm1"
}
],
"availability": "Available with Ubuntu Pro (Infra-only): https://ubuntu.com/pro"
}