Researchers at the Ben-Gurion University of the Negev discovered multiple methods to carry data across two segregated network segments on the same hardware. They achieved this through direct or timing-based covert channels and tested the findings on seven routers in various price ranges from multiple vendors. The methods do not allow exfiltration of large aounts of data but shows that it is possble to break the logical barrier. The researchers tested devices from TP-link, D-Link, Edimax, and Belkin.
Source: https://www.bleepingcomputer.com/news/security/router-network-isolation-broken-by-covert-data-exfiltration/