CVE-2026-66747: Zbtlink CPE2801 Firmware

Critical severity, CVSS 9.8. EPSS: 0.8% chance of exploitation in the next 30 days.

Zbtlink router firmware ships an embedded remote-control implant, ENDLESSDOORS, present in every published build across the product line. It is the open-source ycsunjane/rctl tool built in as an OpenWrt package (librctl.so), started at boot and run as root under the process name kworker to blend in with the kernel's [kworker/*] threads. It opens no listening port; it phones home over cleartext TCP to a hardcoded command-and-control server (command channel 7000, interactive-shell callback 7001) with no authentication and no transport encryption, re-attempting contact roughly every 35 seconds. Its command handler passes any received string to popen() as uid=0, and a reserved rctlbash command returns an interactive root shell. Because the channel is unauthenticated and cleartext, control is not limited to whoever planted it: any party that answers at the C2 address, occupies the network path (DNS or route hijack), or acquires the hardcoded fallback domain obtains unauthenticated remote code execution as root.

Affected products

  • Zbtlink CPE2801 Firmware: version 22.10.09 only
  • Zbtlink WE1026-5g-Wd Firmware: version 21.04.07 only
  • Zbtlink WE1326 Firmware: version 22.02.18_1 only
  • Zbtlink WE2007 Firmware: version 23.08.12 only
  • Zbtlink WE2008-Dsim Firmware: version 23.08.11 only
  • Zbtlink WE2416 Firmware: version 21.03.22_1 only
  • Zbtlink WE3326 Firmware: version 20.09.30 only
  • Zbtlink WE5927 Firmware: version 22.08.10 only
  • Zbtlink WE5931 Firmware: version 22.05.31 only
  • Zbtlink WE5931AC Firmware: version 22.05.31 only
  • Zbtlink WE826-t3-Dsim Firmware: version 21.12.21 only
  • Zbtlink WG108 Firmware: version 21.08.06_1 only
  • Zbtlink WG1602 Firmware: version 23.10.11 only
  • Zbtlink WG1608-Dsim Firmware: version 23.03.16 only
  • Zbtlink WG209 Firmware: version 21.07.28 only
  • Zbtlink WG2105 Firmware: version 22.05.30 only
  • Zbtlink WG2107 Firmware: version 22.09.08 only
  • Zbtlink WG259 Firmware: version 21.03.23 only
  • Zbtlink WG3526 Firmware: version 22.11.01 only
  • Zbtlink Zbt-z8102ax-2sim Firmware: version 7.6.7.2-25.0814_114432 only

Published 2026-08-05. Last modified 2026-09-09.