Tools do more damage than dedicated weapons normally did, the weapons themselves instakill anything that's not a boss. The issue persists after multiple relogs.

How can I get more data on it?

Multiplayer, Singleplayer or LAN?
Cauldron or no Cauldron? (if Multiplayer)
Screenshot and mod list would be appreciated.

Multiplayer, should be normal server unless ATLauncher's servers come bundled with Cauldron or something like it. Only serverside mod installed I know of is Morpheus.

If the issue persisted through server shutdown, I will make screenshots. If it did not, I will repeat the fight.
http://pastebin.com/LjAXn2tr (NEII didn't even pretend to alphabetically sort it. Oh well, presumably it's load order sorted.)
EDIT: Yep, persisted. Have an unenchanted elementium shovel dealing 14 damage.

EDIT 2: NBT playerdata lists generic.attackDamage attribute as having a single modifier, with the following data:

Operation: 2
UUIDLeast: -8449101711440750679
UUIDMost: 7245570952092733273
Amount: 2.6
Name: potion.damageBoost 1

The damage bonus listed is consistent with barehanded punches doing 3-4 damage.

Yeah, seems like a vanilla issue here. All I do is apply the potion itself.