  We classify the Lie algebras of infinitesimal CR automorphisms of weakly
pseudoconvex hypersurfaces of finite multitype in $\mathbb C^N$. In particular,
we prove that such manifolds admit neither nonlinear rigid automorphisms, nor
real or nilpotent rotations. As a consequence, this leads to a proof of a sharp
2-jet determination result for local automorphisms. Moreover, for hypersurfaces
which are not balanced, CR automorphisms are uniquely determined by their
1-jets. The same classification is derived also for special models, given by
sums of squares of polynomials. In particular, in the case of homogeneous
polynomials the Lie algebra of infinitesimal CR automorphisms is always three
graded. The results provide an important necessary step for solving the local
equivalence problem on weakly pseudoconvex manifolds.
