From Halopedia, the Halo wiki
Weapon attachments are devices that can be attached to a firearm, typically on a railing or barrel to increase its functional use.
Some of these attachments include:
Human loadout weapons featured in the Warzone simulation allow for a variety of common attachments that can be swapped between the different weapons including the assault rifle, battle rifle, magnum, SMG, and DMR.
These attachments and their functions are as follows: