Extra Attachment is a perk featured in Call of Duty: Ghosts. It allows the player to equip a third attachment to their primary weapon and a second attachment to their secondary, similarly to the Primary Gunfighter and Secondary Gunfighter wildcards from Call of Duty: Black Ops II, Call of Duty: Advanced Warfare and Call of Duty: Black Ops III.
Even with Extra Attachment equipped, the same limit of one attachment per attachment group still applies.
Extra Attachment is most useful on multi-purpose weapons, such as assault rifles or light machine guns. One could, for example, add Armor-Piercing rounds to a light machine gun already equipped with a Foregrip and an optical attachment, to add extra punch against armor and pointstreaks, without compromising the accuracy of the weapon. The perk is less useful on more specialized weapons, such as Shotguns or Pistols, as they generally don't require more than two attachments to be effective. It is completely ineffective on the Riot Shield, which is restricted to mod attachments, and the VKS, which only has two groups of attachments. Extra Attachment is most useful on classes using a primary and secondary weapon, with the perk granting one extra attachment to each weapon.
Weapons with integral attachments, such as the Honey Badger and the CBJ-MS can benefit even more from the perk, effectively having a possible total of four attachments. The CBJ-MS, MSBS and Gold PDW are unique in the aspect that they can be equipped with two Mod attachments, since each of the weapons have one mod attachment integrated into them. The Maverick-A2 can also combine the Variable Zoom Scope with its integral Tracker Scope, similarly to sniper rifles in Call of Duty: Black Ops II being able to use the Variable Zoom in tandem with the Dual Band Scope. Using these weapons in tandem with Extra Attachment can be done to speed up progression towards various challenges by allowing for more challenges to be worked towards.