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CVE-2026-18685 – Unauthenticated Command Injection (RCE) – GL.iNet GL-MT3000 (Beryl AX) firmware 4.4

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Summary

CVE-2026-18685 is an unauthenticated command injection vulnerability in GL.iNet GL-MT3000 (Beryl AX) routers. The flaw resides in the set_upgrade function exported by the modem.so library and reachable through the /cgi-bin/glc endpoint, allowing a remote attacker to execute arbitrary commands as root without credentials. It is rated Critical.

Technical details

  • Root cause: The set_upgrade handler in modem.so embeds the attacker-controlled firmware_upload parameter directly into a shell command via sprintf() without quoting or sanitization, and executes it through /bin/sh -c. The existence check performed before this validates the modem_url value but not firmware_upload.
  • Trigger conditions: An attacker sends a crafted JSON request to /cgi-bin/glc invoking object=modem, method=set_upgrade, with shell metacharacters (for example &(command);#) placed in the firmware_upload field.
  • Attack vector: Network — reachable remotely over HTTP against the device’s web interface, requiring no authentication and no user interaction (CWE-77 / CWE-74 command injection).
  • Impact: Arbitrary command execution with root privileges, leading to full compromise of confidentiality, integrity, and availability of the device.

Affected software

  • GL.iNet GL-MT3000 (Beryl AX) firmware versions 4.4.0 through 4.4.5.

Severity

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

Mitigation and recommended actions

  • Immediate: Update GL-MT3000 devices to the latest firmware available from GL.iNet’s official firmware and security-updates channels, and verify the running version is no longer within the 4.4.0–4.4.5 range.
  • If no patch can be applied yet: Do not expose the router’s web/administration interface (/cgi-bin/glc) to the internet. Restrict management access to trusted LAN clients or a VPN, and place the device behind a firewall that blocks inbound access to the HTTP interface from untrusted networks.

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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1

Map your entire attack surface (continously)

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4

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Results are routed through integrations with ticketing, SOAR, and SIEM tools. Issues are written in plain language, bundled into remediation clusters, and prioritized based on asset criticality, exploitability, and blast radius. This shortens mean time to remediation (MTTR) and empowers teams to act with confidence.

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