Source https://makandracards.com/makandra/35943-terminal-escape-sequences-the-new-xss-for-linux-sysadmins

$ printf '#!/bin/bash\necho doing something evil!\nexit\n\033[2Aecho doing something very nice!\n' > backdoor.sh

$ chmod +x backdoor.sh

$ cat backdoor.sh
#!/bin/bash
echo doing something very nice!

$ ./backdoor.sh
doing something evil!