A path traversal vulnerability exists in numerous routers manufactured by multiple vendors using Arcadyan based software. This vulnerability allows an unauthenticated user access to sensitive information and allows for the alteration of the router configuration.
The vulnerability, identified as CVE-2021-20090, is a path traversal vulnerability. An unauthenticated attacker is able to leverage this vulnerability to access resources that would normally be protected. The researcher initially thought it was limited to one router manufacturer and published their findings, but then discovered that the issue existed in the Arcadyan based software that was being used in routers from multiple vendors.
Successful exploitation of this vulnerability could allow an attacker to access pages that would otherwise require authentication. An unauthenticated attacker could gain access to sensitive information, including valid request tokens, which could be used to make requests to alter router settings.
The CERT/CC recommends updating your router to the latest available firmware version. It is also recommended to disable the remote (WAN-side) administration services on any SoHo router and also disable the web interface on the WAN.