CVE-2026-66747
Status: DeferredCritical (9.3)—
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.
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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.
CVSS
- Version: 4.0
- 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/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X
- Base score: 9.3
Exploitation probability (EPSS)
- Probability of exploitation in the next 30 days: 0.79%
- Percentile among all scored CVEs: 55
- Score date: 10/1/2026
EPSS (Exploit Prediction Scoring System, FIRST) estimates how likely a vulnerability is to be exploited in the wild within 30 days. It complements CVSS (impact) and CISA KEV (confirmed exploitation).
Affected technologies (2)
⚠ AI-inferred from the description — NVD hasn't analyzed this CVE yet, these aren't verified CPEs.
CWEs
- CWE-506
References
Raw JSON (NVD)
Show
{
"id": "CVE-2026-66747",
"cveTags": [],
"metrics": {
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{
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{
"cpes": [
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{
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"product": "WE3326 Firmware",
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{
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{
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{
"cpes": [
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"product": "WG3526 Firmware",
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{
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"vendor": "Zbtlink",
"product": "ZBT-Z8102AX-2SIM Firmware",
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],
"published": "2026-08-05T11:16:25.510",
"references": [
{
"url": "https://github.com/ycsunjane/rctl",
"source": "disclosure@vulncheck.com"
},
{
"url": "https://www.vulncheck.com/advisories/zbt-endlessdoors",
"source": "disclosure@vulncheck.com"
},
{
"url": "https://www.vulncheck.com/blog/zbt-endlessdoors",
"source": "disclosure@vulncheck.com"
},
{
"url": "https://www.zbtlink.com/pages/zbt-router-firmware-download",
"source": "disclosure@vulncheck.com"
}
],
"vulnStatus": "Deferred",
"weaknesses": [
{
"type": "Secondary",
"source": "disclosure@vulncheck.com",
"description": [
{
"lang": "en",
"value": "CWE-506"
}
]
}
],
"descriptions": [
{
"lang": "en",
"value": "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."
}
],
"lastModified": "2026-09-09T20:35:08.537",
"sourceIdentifier": "disclosure@vulncheck.com"
}