Opener Saim Ayub and captain Salman Agha were both out for first-ball ducks, while Pakistan failed to kick on from 102-2 after Haris dragged on to left-arm spinner Aamir Kaleem, who took 3-31, in the 13th over.
Oman, who qualified for the last T20 World Cup and will play in the Asia qualifier for a place at 2026 tournament next month, reached 41-2 in reply, but lost their next seven wickets for 10 runs and the remaining eight for 26.
Seamer Faheem Ashraf took 2-6, wrist spinner Sufiyan Muqeem 2-7 and Ayub 2-8 with his off-spin.
Pakistan, who left former captains Babar Azam and Mohammad Rizwan out of their squad, play rivals India in Dubai on Sunday.
