Is the attack roll to splash holy water or oil on a target within 5 feet of you made with disadvantage?

Question

The description of holy water (flask) states:

As an action, you can splash the contents of this flask onto a creature within 5 feet of you or throw it up to 20 feet, shattering it on impact. In either case, make a ranged attack against a target creature, treating the holy water as an improvised weapon.

The description of oil (flask) reads similarly.

Is the attack roll made to splash the contents of the flask onto a creature within 5 feet of you made with disadvantage? If so, is there any meaningful difference between splashing the contents or throwing and shattering the flask?

Answer 1

Yes, the attack is made at disadvantage; the only difference is what happens to the flask

As stated in your quote, regardless of whether you splash the contents of the flask at a creature within 5 feet or throw it at a creature up to 20 feet away, you make a ranged attack.

The rule on making a ranged attack with an enemy within 5 feet of you says:

Aiming a ranged attack is more difficult when a foe is next to you. When you make a ranged attack with a weapon, a spell, or some other means, you have disadvantage on the attack roll if you are within 5 feet of a hostile creature who can see you and who isn't incapacitated.

(One of the benefits of the Crossbow Expert feat (PHB, p. 165) is to eliminate this disadvantage.)

The only apparent reason the two methods of making this ranged attack are called out separately is what happens to the flask when you make the attack. If you splash the contents of the flask onto a creature 5 feet away, the flask remains intact and in your hand; only its contents (holy water or oil) are splashed onto the creature. On the other hand, if you throw the flask at the creature, it shatters on impact and can't be recovered, causing its contents to splash against the target if it hits.

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As Akixkisu's answer notes, oil can also be poured onto the ground directly and lit on fire that way:

You can also pour a flask of oil on the ground to cover a 5-foot-square area, provided that the surface is level. If lit, the oil burns for 2 rounds and deals 5 fire damage to any creature that enters the area or ends its turn in the area.

And holy water can also be poured on the ground directly to purify desecrated ground (DMG, p. 110):

A vial of holy water purifies a 10-foot-square area of desecrated ground when sprinkled on it, and a hallow spell purifies desecrated ground within its area.

Neither of these is an attack, and they involve no rolls. In the absence of anything specifying whether they take an action, this can likely be done with a free object interaction, or the Use an Object action if that has already been used.

Answer 2

The attack is usually made at a disadvantage because it is a ranged attack in close combat, and you may choose to sprinkle the holy water on the ground instead of attacking.

Regardless of how you attack, either by throwing the liquid or the flask, you make a ranged attack.

In either case, make a ranged attack

Ranged Attack in Close Combat, PHB 195 (emphasis mine):

Aiming a ranged attack is more difficult when a foe is next to you. When you make a ranged attack with a weapon, a spell, or some other means, you have disadvantage on the attack roll if you are within 5 feet of a hostile creature who can see you and who isn't incapacitated.

There is also the possibility of pouring the flask on the ground compare the effects of a flask of oil with the rules of desecrated ground:

You can also pour a flask of oil on the ground to cover a 5-foot-square area, provided that the surface is level.

Desecrated Ground, DMG 110:

A vial of holy water purifies a 10-foot-square area of desecrated ground when sprinkled on it, and a hallow spell purifies desecrated ground within its area.

If you make a ranged attack within 5 feet of you, you splash the content of the flask. The flask stays intact. If you make a ranged attack by throwing up to 20 feet, the flask shatters on impact. If you pour the flask on the ground you have not made an attack, and the flask stays intact.