We're allowed self-defense and punishment, according to Kant (indeed, it is required). It may, for example, be acceptable to lie to a murderer if he lies to you, since we are obligated to punish those who violate the CI. (EDIT: It could also mean that we don't have to say anything to murderers, we aren't obligated to tell the truth in every situation, but we are obligated to tell the truth in every case where we tell something. )

That said, I'm not not sure exactly what you mean by the original line "Kant only defended the duty not to lie out of philanthropic concerns". It could mean, "Kant defended the duty not to lie, but his reasons for this duty were mere philanthropic ones." It could also mean "With respect to truth-telling, Kant only says we have a duty when we might prefer to lie for philanthropic reasons." Both interpretations are wrong. Here is a quote from Kant's explicit tackling of the issue in the appropriately titled "On a supposed right to lie from philanthropy." Apologies for the long quote but I don't want to have to debate context.

Truthfulness in statements that one cannot avoid is a human being's duty to everyone, however great the disadvantage to him or to another that may result from it... If I falsify... I... do wrong in the most essential part of duty in general by such falsification... that is, I bring it about, as far as I can, that statements (declarations) in general are not believed, and so too that all rights which are based on contracts come to nothing and lose their force; and this is a wrong inflicted upon humanity generally... For a lie always harms another, even if not another individual, nevertheless humanity generally, inasmuch as it makes the source of right unusable. ---- "On a supposed right to lie from philanthropy", Berliner Blätter, September 1797