Multiple buffer overflows in the limited configuration shell (/sbin/gs_config) on Grandstream HT801 devices before 1.0.29 allow remote authenticated users to execute arbitrary code as root via a crafted manage_if setting, thus bypassing the intended restrictions of this shell and taking full control of the device. There are default weak credentials that can be used to authenticate.
https://www.secforce.com/blog/exploiting-grandstream-ht801-ata-cve-2021-37748-cve-2021-37915/
https://github.com/SECFORCE/CVE-2021-37748
http://www.grandstream.com/products/gateways-and-atas/analog-telephone-adaptors/product/ht801