The impossibility of faster-than-light relative speed only applies locally. Wormholes might allow effective superluminal (
faster-than-light) travel by ensuring that the speed of light is not exceeded locally at any time. While traveling through a wormhole, subluminal (slower-than-light) speeds are used. If two points are connected by a wormhole whose length is shorter than the distance between them
outside the wormhole, the time taken to traverse it could be less than the time it would take a light beam to make the journey if it took a path through the space
outside the wormhole. However, a light beam traveling through the wormhole would of course beat the traveler.