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CVE-2026-18686 – Pre-Authentication Command Injection (RCE) – GL.iNet GL-MT3000 firmware 4.4.0 throu

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Summary

CVE-2026-18686 is a pre-authentication command injection vulnerability in the nas-web RPC wrapper of GL.iNet GL-MT3000 (Beryl AX) routers. An unauthenticated, network-based attacker can inject shell commands that execute as root, leading to remote code execution and full device compromise. The issue is rated critical (CVSS v4.0 9.3).

Technical details

  • Root cause: A two-stage (second-order) injection flaw in the nas-web RPC interface exposed at /cgi-bin/glc. The nas-web.add_user method writes the supplied password value into the nas_user table of /etc/config/gl_nas/file_share.db without sanitization or shell escaping.
  • Trigger conditions: A subsequent call to nas-web.add_share with proto=samba and the previously created user in the users[] array retrieves the stored password and passes it into a shell command (smbpasswd) via the backend service gl_nas_sys, executing it without escaping.
  • Attack vector: Network, unauthenticated — both nas-web.add_user and nas-web.add_share are reachable without credentials and require no user interaction.
  • Impact: Blind command execution with root privileges, enabling full compromise of confidentiality, integrity, and availability. Because the payload is stored, exploitation can be staged over time.

Affected software

  • GL.iNet GL-MT3000 (Beryl AX) firmware versions 4.4.0, 4.4.1, 4.4.2, 4.4.3, 4.4.4, and 4.4.5.

Severity

  • CVSS v4.0 base score: 9.3 (Critical) — 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
  • CVSS v3.1 base score: 9.8 (Critical) — Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

Mitigation and recommended actions

  • Immediate: Upgrade to a firmware release later than 4.4.5 once available from GL.iNet, and monitor the vendor’s security update channel for the fixed build.
  • If no patch: Do not expose the router’s web/administration and NAS interfaces to the internet. Restrict access to /cgi-bin/glc to trusted management networks, disable the Samba/NAS file-sharing feature if not required, and place the device behind a firewall that blocks inbound access to management and NAS ports.

How IONIX identifies potentially affected assets

IONIX matches the following signals against data already collected when it crawled the asset; identifying the technology sends no request beyond that crawl.

  • Page title: GL.iNet, GL-MT3000, Beryl AX, GL.iNet Admin Panel

References

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