CVE-2026-66747 (CVSS 9.8)

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.

Is your site exposed to CVE-2026-66747?

Run a free security scan — no signup, results in seconds.

CVSS v3.1 Score

9.8

CRITICAL

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

EPSS — Exploit Prediction

0.0066

Probability of exploitation

0.49%

Percentile rank

EPSS estimates the probability that this vulnerability will be exploited in the wild within the next 30 days. A higher score means more likely to be exploited.

Weakness Type (CWE)

CWE-506 CWE-506

References

Other References

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

Frequently Asked Questions

What is CVE-2026-66747? +

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. It has a CVSS v3.1 base score of 9.8 (CRITICAL).

How severe is CVE-2026-66747? +

CVE-2026-66747 has a CVSS v3.1 score of 9.8 out of 10, rated CRITICAL. This is a critical vulnerability that should be patched immediately. The EPSS score is 0.0066, placing it in the 0th percentile for exploitation probability.

How do I check if I'm vulnerable to CVE-2026-66747? +

You can use Secably's free Website Scanner to check your website for known vulnerabilities. For infrastructure scanning, use the Port Scanner to identify exposed services that may be affected. Check the vendor advisories linked above for specific patch and version information.

Related Vulnerabilities

CVE-2025-59141

simple-swizzle swizzles function arguments. On 8 September 2025, the npm publishing account for simple-swizzle was taken over after a phishing …

CVE-2025-59142

color-string is a parser and generator for CSS color strings. On 8 September 2025, the npm publishing account for color-string …

CVE-2017-20203

NetSarang Xmanager Enterprise 5.0 Build 1232, Xmanager 5.0 Build 1045, Xshell 5.0 Build 1322, Xftp 5.0 Build 1218, and Xlpd …

CVE-2025-32965

xrpl.js is a JavaScript/TypeScript API for interacting with the XRP Ledger in Node.js and the browser. Versions 4.2.1, 4.2.2, 4.2.3, …

CVE-2025-59140

backlash parses collected strings with escapes. On 8 September 2025, the npm publishing account for backslash was taken over after …

CVE-2018-25117

VestaCP commit a3f0fa1 (2018-05-31) up to commit ee03eff (2018-06-13) contain embedded malicious code that resulted in a supply-chain compromise. New …

CVE-2026-66747