As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
AIRCRAFT WAS GROUNDED: FLIGHT RETURNED TO PHL ON ACCOUNT OF BOTH AFT FLIGHT ATTENDANT OXYGEN MASKS DEPLOYED. AN EMERGENCY WAS DECLARED AND THE FLIGHT LANDED OVERWEIGHT WITHOUT INCIDENT. MAINTENANCE REMOVED & REPLACED AFT FA O2 BOXES IAW AMM 35-20-05. OPS CK GOOD IAW AMM 35-20-00.