A critical authentication bypass vulnerability in GL.iNet 4.x firmware allows unauthenticated attackers to gain full administrative control of the device.

The vulnerability is an authentication bypass flaw triggered by providing a username that is simultaneously a valid SQL statement and a valid regular expression. This grants the attacker full administrative access without prior authentication.

With a CVSS score of 9.8, this flaw is extremely critical as it allows full administrative control over network infrastructure devices. An attacker could intercept traffic, modify network settings, or pivot into the local network, leading to complete compromise of the affected environment.

Immediate Action: Check the manufacturer's support portal for the latest firmware release beyond 4.3.7 and apply it immediately.

Proactive Monitoring: Monitor device access logs for unusual login attempts and audit all administrative accounts for unauthorized modifications.

Compensating Controls: Disable remote administrative access (WAN access) to the device's web interface immediately and ensure management is only performed over trusted local segments.

Public Exploit Available: Yes — a proof-of-concept is available on GitHub.

Given the ease of exploitation and the potential for total device takeover, this vulnerability represents an urgent risk. Users must verify their firmware version and apply the latest available updates from GL.iNet immediately to secure their network devices.