The eighth cortex was supposedly the final level of shaping protocols available to the Yuuzhan Vong. Only the Supreme Overlord knew what was in the eighth cortex, and saw fit as to when he should distribute the information to the Shaper caste. Through the Supreme Overlord the gods of the Yuuzhan Vong supposedly dispensed the protocols.
In reality, by the time of the Yuuzhan Vong War of 25 ABY, the eighth cortex was still empty. There were no new protocols explaining how to defeat the tenacious, versatile infidels who populated the galaxy. The shaper Onimi had seen this and had sought to fill the eighth cortex. His experiments failed, transforming him into a Shamed One. He manipulated his puppet Shimrra into allowing the heretic Nen Yim to design new protocols herself. The damutek of the eighth cortex was located on Yuuzhan'tar. As the war continued, heresy among the shapers spread, as the yammosk jammers, holocomm networks and Jedi proved problematic.
The discovery that the eighth cortex was and had always been empty was one of the factors contributing to the Executor Nom Anor becoming the heretic prophet Yu'shaa.