Jesus is the only possible path to salvation. The Church is the Body of Christ, the temple of God where we encounter Christ and get grafted onto Him. Therefore there is no salvation outside the Church, because salvation is the Church.
The issue, of course, is to define where the boundaries of the Church begin and end. At the very least, the boundaries of the Church end at proper doctrine concerning who Jesus is.
Peter confesses that Jesus is truly God and truly man, and Jesus immediately links this to the foundation of the Church. St Paul warns the Church of Rome that they were grafted onto Israel for having faith in Christ, but if they cease to have faith they will be cut off, like the unbelieving Jews. Jesus permits some people to exorcise using His name even though they don't follow the apostles, because whoever uses His name (that is, believes properly about who He is) cannot speak ill of Him, but in contrast we see some unbelieving Jews in the book of Acts try to exorcize using Jesus' name and fail completely.
But that's about where the consensus ends. Sure, having the true faith is what defines where the Church is, but what are the implications? Catholics would say that, since the Pope is the successor of Peter and the sole infallible guardian of the faith, one must be in communion with the Pope to be in the Church. Orthodox would say that one must be under a canonical bishop to be in the Church, since only canonical bishops can give the sacraments which are how we encounter Christ (and for a bishop to be canonical, he must be recognized as Orthodox by the other bishops and himself agree to the 7 ecumenical councils). Protestants are a varied bunch - some consider that there is no true Christian faith apart from their denomination, some consider that the points of the Reformation (justification by faith alone, etc) are essential to the gospel and therefore Catholics and Orthodox aren't in the Church, and some consider that simply believing in Jesus in any capacity is sufficient.
With all this being said, there is also the motto of "we know where the Church is but not where it is not", which some may or may not agree with.