# CVE-2026-66747

## Summary

- **CVE ID:** CVE-2026-66747
- **Severity:** CRITICAL
- **CVSS Score:** 9.8 (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)
- **CWE:** CWE-506
- **Published:** Aug 5, 2026
- **Last Modified:** Aug 5, 2026

## 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.

## Affected Products

- 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)

## References

- [CNA](https://www.vulncheck.com/blog/zbt-endlessdoors)
- [CNA](https://www.zbtlink.com/pages/zbt-router-firmware-download)
- [CNA](https://github.com/ycsunjane/rctl)
- [CNA](https://www.vulncheck.com/advisories/zbt-endlessdoors)

## Exploitation Prediction (EPSS)

- **EPSS Score:** 0.66%
- **EPSS Percentile:** 49.4

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_Exported from OnDuty AI Vulnerability Intelligence on 2026-09-11._