Raw 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:XCVSS and EPSS are reproduced from their sources (NVD, FIRST EPSS). Risk Priority is our own derived reading, not an NVD score.
Summary
CVE-2026-66747 is a critical-severity Embedded Malicious Code (CWE-506) vulnerability in Zbtlink (inferred from references). Its CVSS base score is 9.3 (Critical).
Operationally, exploitation aligns with the MITRE ATT&CK technique Embedded Payloads (T1027.009); ranked at the 50th percentile by exploit likelihood (below the median); it is not currently listed in the CISA KEV catalog; a public proof-of-concept is referenced.
The strongest mitigations our analysis identified map to SA-11 (Developer Testing and Evaluation) and SC-44 (Detonation Chambers) — see the control section below for these in your framework.
OWASP Top 10 for Web (2025)
EU & UK References
- 🇪🇺 ENISA EUVD: EUVD-2026-53301
Vulnerability Data
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…
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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.
- CWE(s)
Related Threats
MITRE ATT&CK Enterprise Techniques
CVEs Like This One
Affected Assets
Mitigating Controls
Control response
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- 3 hardening rules · 2 OS baselines
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Mitigating Controls (NIST 800-53 r5) AI
Developer testing and evaluation can discover embedded malicious code before release.
Detonation chambers can reveal embedded malicious code through controlled execution analysis.
Integrity verification tools directly detect unauthorized or malicious code insertions.
Tamper-resistance and detection mechanisms identify malicious code introduced via the supply chain.
Component authenticity requirements reduce the chance malicious code is embedded by developers or suppliers.
Component authenticity controls stop introduction of malicious or counterfeit code into the product.
Mitigating Controls (NIST CSF 2.0) AI
Derived directly from the weakness types (CWEs) cited in the NVD entry via our AI-authored CWE→CSF cross-walk (authority under review) — links open the control.
Due diligence prior to supplier relationships helps avoid sources of embedded malicious code.
Supplier risk assessment reduces likelihood of receiving products containing malicious code.
Assessing authenticity and integrity before acquisition catches embedded malicious code.
Pre-acquisition assessment of critical suppliers mitigates risk of malicious code in procured software.
Secure SDLC practices directly prevent introduction of malicious code during development.
Mitigating Controls (ISO/IEC 27001:2022 Annex A) AI
Derived directly from the weakness types (CWEs) cited in the NVD entry via our AI-authored CWE→ISO cross-walk (authority under review) — links open the control.
Requiring suppliers to furnish component lists, attestations, and cryptographic verification of delivered artefacts makes it harder for an attacker to embed hidden malicious code that would otherwise go undetected through the supply chain.
Checks that executed code has not been tampered with and monitoring for malware-associated activity reduce the likelihood that hidden malicious code remains active.
Hardening callouts derived
Configuration rules from DISA STIG baselines that bear on weaknesses of the type cited by this CVE. Each rule is shown with the relationship its mapping actually records, against the CWE it was authored against. Derived via CVE→CWE over `controls_xwalks` (higher-evidence rows only; rows rated `none` are excluded).
Oracle Linux 9 (1 rule)
- V-271452 OL 9 must use a Linux Security Module configured to enforce limits on system services. prevents CWE-506
RHEL 9 (1 rule)
- V-258078 RHEL 9 must use a Linux Security Module configured to enforce limits on system services. prevents CWE-506