A vulnerability in Mitel 6900 Series IP (MiNet) phones excluding 6970, versions 1.8 (1.8.0.12) and earlier, could allow a unauthenticated attacker with physical access to the phone to gain root access due to insufficient access control for test functionality during system startup. A successful exploit could allow access to sensitive information and code execution.
https://www.mitel.com/support/security-advisories/mitel-product-security-advisory-22-0003
https://www.mitel.com/support/security-advisories
http://seclists.org/fulldisclosure/2022/Jun/32
http://packetstormsecurity.com/files/167547/Mitel-6800-6900-Series-SIP-Phones-Backdoor-Access.html