The 31 August 2025 Mw 5.9 Asadabad earthquake in eastern Afghanistan caused severe damage despite its moderate magnitude, raising questions about rupture processes and seismic hazard in the southern Hindu Kush. Using Sentinel-1 InSAR and teleseismic waveform modeling, we reveal a complex, multi-stage shallow (4–5 km) rupture involving the mainshock and three M > 5.0 aftershocks. Surface deformation ranges from ~10 to 35 cm, and fault planes exhibit moderate to steep dip angles, with secondary rupture approaching the surface. Time-series InSAR shows ~2 mm/yr localized interseismic uplift near the epicenter, consistent with localized shallow deformation prior to the earthquake. Occurring within exposed crystalline basement rocks without mapped Quaternary faults, the earthquake ruptured a previously unknown immature, distributed fault system. These findings help explain the high damage relative to magnitude and highlight significant seismic hazard in orogenic interiors from moderate-magnitude, shallow ruptures on unmapped faults.