Pi-hole: Local privilege escalation from `pihole` user to root via CVE-2026-41489 fix bypass

Pi-hole is a DNS sinkhole that protects devices from unwanted content without installing any client-side software. Prior to 6.5, advanced/Scripts/utils.sh getFTLPID() attempts to validate the pihole-owned /run/pihole-FTL.pid file with expr "${FTL_PID}" : "[^[:digit:]]", but this rejects only values whose first character is not a digit. An attacker with code execution as the pihole user can write a digit-prefixed arithmetic expression to the pihole-owned PID file. Root-run pihole subcommands then evaluate [[ "$pid" -eq "-1" ]], causing Bash to recursively evaluate array subscripts and execute command substitution as root. This bypasses the content-validation portion of the CVE-2026-41489 remediation while leaving its hardcoded PID-file path protection intact. This issue is fixed in version 6.5.