Critical exploit reference

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

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.

Published Aug 5, 2026 · Updated Oct 15, 2026 · Sources: NIST National Vulnerability Database, CVE Program (cve.org) e CISA ADP · CNA: VulnCheck

Low

Who exploits it and how urgent it is

A 0–100 score combining confirmed exploitation, ransomware and APT use, public exploits, EPSS and severity.

No exploitation signal in the sources consulted so far.

How the score was calculated

Technical severity (critical)+10
CISA SSVC: exploitation "poc"+5
Automatable exploitation (SSVC)+3

The score orders the patch queue; it does not replace your asset context (internet exposure, criticality, compensating controls).

Triage

Is it exploited, how likely is exploitation, what does it touch, and how severe do the sources call it.

Exploitation

Not confirmed

Not in CISA KEV — an absence of record, not proof it is unexploited.

EPSS FIRST

—

No EPSS score.

Affects

Zbtlink

CPE2801 Firmware and 19 more

CVSS base

9.8

Critical · 2 source(s)

CISA SSVC assessment CISA

Three decision points CISA publishes for the CVEs it assesses (SSVC 2.0.3). A stakeholder decision, not a severity score.

Exploitation

Proof of concept

none · proof-of-concept · active

Automatable

Yes

can an attacker script the kill-chain steps

Technical impact

Total

partial · total control of the vulnerable component

Remediation

Fixes and mitigations documented by the sources — linked to the original advisory.

No fix documented by the sources we poll. That does not mean none exists: check the vendor advisory.

First 24 hours

Ordered from the record’s own fields — exposure first, because you cannot patch what you have not found. A rule-generated starting point.

Identify exposed assets running the affected vendor/product/version combinations (Zbtlink CPE2801 Firmware, Zbtlink WE1026-5G-WD Firmware, Zbtlink WE1326 Firmware…).
The attack is network-based and needs no privileges: restrict exposure (ACLs, VPN, WAF) until patched.
No fix documented in the sources: reduce exposure and monitor the vendor advisory.
Search available logs for exploit probes, errors and authentication anomalies.

Affected scope

Vendor, product and versions as the sources word them.

Vendor	Product	Versions	Status	Source
Zbtlink	CPE2801 Firmware	version 22.10.09	Vulnerable	CVE Program (cve.org) e CISA ADP
Zbtlink	WE1026-5G-WD Firmware	version 21.04.07	Vulnerable	CVE Program (cve.org) e CISA ADP
Zbtlink	WE1326 Firmware	version 22.02.18_1	Vulnerable	CVE Program (cve.org) e CISA ADP
Zbtlink	WE2007 Firmware	version 23.08.12	Vulnerable	CVE Program (cve.org) e CISA ADP
Zbtlink	WE2008-DSIM Firmware	version 23.08.11	Vulnerable	CVE Program (cve.org) e CISA ADP
Zbtlink	WE2416 Firmware	version 21.03.22_1	Vulnerable	CVE Program (cve.org) e CISA ADP
Zbtlink	WE3326 Firmware	version 20.09.30	Vulnerable	CVE Program (cve.org) e CISA ADP
Zbtlink	WE5927 Firmware	version 22.08.10	Vulnerable	CVE Program (cve.org) e CISA ADP
Zbtlink	WE5931 Firmware	version 22.05.31	Vulnerable	CVE Program (cve.org) e CISA ADP
Zbtlink	WE5931AC Firmware	version 22.05.31	Vulnerable	CVE Program (cve.org) e CISA ADP
Zbtlink	WE826-T3-DSIM Firmware	version 21.12.21	Vulnerable	CVE Program (cve.org) e CISA ADP
Zbtlink	WG108 Firmware	version 21.08.06_1	Vulnerable	CVE Program (cve.org) e CISA ADP
Zbtlink	WG1602 Firmware	version 23.10.11	Vulnerable	CVE Program (cve.org) e CISA ADP
Zbtlink	WG1608-DSIM Firmware	version 23.03.16	Vulnerable	CVE Program (cve.org) e CISA ADP
Zbtlink	WG209 Firmware	version 21.07.28	Vulnerable	CVE Program (cve.org) e CISA ADP
Zbtlink	WG2105 Firmware	version 22.05.30	Vulnerable	CVE Program (cve.org) e CISA ADP
Zbtlink	WG2107 Firmware	version 22.09.08	Vulnerable	CVE Program (cve.org) e CISA ADP
Zbtlink	WG259 Firmware	version 21.03.23	Vulnerable	CVE Program (cve.org) e CISA ADP
Zbtlink	WG3526 Firmware	version 22.11.01	Vulnerable	CVE Program (cve.org) e CISA ADP
Zbtlink	ZBT-Z8102AX-2SIM Firmware	version 7.6.7.2-25.0814_114432	Vulnerable	CVE Program (cve.org) e CISA ADP

Attack characteristics

The CVSS vector, decoded. It describes the attack, not your exposure to it.

Attack vector

Network

Attack complexity

Low

Privileges required

None

User interaction

None

Scope

Unchanged

Confidentiality

High

Integrity

High

Availability

High

Every base score collected

Sources score independently and may disagree; each row says who scored it and under which version.

Score	Version	Severity	Expl.	Impact	Scored by
9.3	CVSS 4.0	Critical	—	—	disclosure@vulncheck.com via NIST National Vulnerability Database
9.3	CVSS 4.0	Critical	—	—	VulnCheck via CVE Program (cve.org) e CISA ADP
9.8	CVSS 3.1	Critical	3.9	5.9	disclosure@vulncheck.com via NIST National Vulnerability Database
9.8	CVSS 3.1	Critical	—	—	VulnCheck via CVE Program (cve.org) e CISA ADP

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H (score shown at the top: disclosure@vulncheck.com)

Weakness MITRE

Weakness class according to MITRE’s CWE catalog.

CWE-506

Other CVEs with this weakness →

Detection

Read off the CVSS vector and the weakness class. Starting points, not tested rules.

Prioritize edge telemetry for the network-reachable component (proxy, WAF, IDS/IPS).

web/proxy/WAF logsnetwork IDS/IPS

Timeline

What happened to this CVE, newest first.

2026
Affected products added · zbtlink/cpe2801 firmware, zbtlink/we1026-5g-wd firmware, zbtlink/we1326 firmware, zbtlink/we2007 firmware, zbtlink/we200
Oct 15, 2026 · CVE Program (cve.org) e CISA ADP
SSVC assessment updated
Oct 15, 2026 · CVE Program (cve.org) e CISA ADP
Record published
Oct 15, 2026
CVSS changed · 9.8
Oct 15, 2026 · NIST National Vulnerability Database
Source status changed · → Deferred
Oct 15, 2026 · NIST National Vulnerability Database
Record created in this database
Oct 15, 2026 · NIST National Vulnerability Database
CVE published
Aug 5, 2026 · VulnCheck

Source activity

Repeated readings are counted rather than listed.

1× Official description updated · Oct 15, 2026 – Oct 15, 2026

References

4 on the record

www.vulncheck.com/blog/zbt-endlessdoors
technical-description, exploit, NIST National Vulnerability Database
github.com/ycsunjane/rctl
NIST National Vulnerability Database
www.zbtlink.com/pages/zbt-router-firmware-download
product, NIST National Vulnerability Database
www.vulncheck.com/advisories/zbt-endlessdoors
third-party-advisory, NIST National Vulnerability Database

Elsewhere on this site

Zbtlink
every CVE for this vendor

CWE-506
other pages naming this weakness

Not in any source we poll

Listed rather than left blank: an empty field and an unmeasured one look identical on screen, and only one is a reason to look elsewhere.

No FIRST EPSS score.
No fixed version, patch or mitigation documented.
No confirmed IOCs, IP addresses, domains, file hashes, or malware artifacts supplied.
No organization-specific asset inventory, compensating-control status, or patch deployment evidence supplied.
No exploit packet captures, log samples, or incident case IDs supplied.

Answered from this record

Text assembled only from the fields above — no additional claims.

What should defenders know first?

CVE-2026-66747 is "ENDLESSDOORS: Zbtlink Router rctl/kworker Phone-Home Root Implant", rated Critical. It affects CPE2801 Firmware (Zbtlink); versions are in the scope table. It is not in CISA KEV, which does not rule out exploitation. CVSS 9.8 describes technical severity. First verify whether exposed or business-critical assets run the affected versions, apply vendor fixes or mitigations, and preserve logs for review.

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