The linear stability analysis of hypersonic flow over a sharp slender cone with an attached shock is described. Attention is focused on the viscous modes of instability which may be described by a triple-deck structure. The situation in which both the effect of the shock and the influence of curvature are important is considered in the weak-interaction region. Both neutral and non-neutral solutions are presented for both axisymmetric and non-axisymmetric disturbances. The results obtained suggest that the effect of curvature on the stability of hypersonic flow is significant when the attached shock is taken into account.