CVE-2026-66747 ENDLESSDOORS: Zbtlink Router rctl/kworker Phone-Home Root Implant
Zbtlink routers contain a hardcoded root backdoor that phones home to a C2 server, allowing remote code execution via network hijacking or C2 takeover.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- None listed
What is CVE-2026-66747?
CVE-2026-66747 is a critical vulnerability in Zbtlink CPE2801 Firmware, published on 5 Aug 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Official description
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.
Weakness: CWE-506
Which versions are affected by CVE-2026-66747?
How do I fix CVE-2026-66747?
No fix has been published for CVE-2026-66747 yet. Limit exposure of the affected software until one is available.
Is CVE-2026-66747 being exploited?
It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-66747 exists.
Public exploit code: 1 proofs of concept on GitHub.
Sources
Also known as GHSA-gf5q-q6h6-j87v.