Sunhillo SureLine before 9.1.5 contains an OS command injection vulnerability in the networkDiag.cgi endpoint that allows an authenticated remote attacker with any web account to execute arbitrary commands as root by injecting shell metacharacters into the ipAddr or dnsAddr parameters. Attackers can bypass the incomplete character denylist from the prior CVE-2021-36380 fix using URL-encoded newline (%0a) or ampersand (%26) sequences that act as command separators after decoding in the ping, nslookup, or traceroute diagnostic modes, leading to full system compromise.