#!/usr/bin/env bash
# Host policy helpers (allow/deny lists, normalization, private IP checks).
set -euo pipefail
mcp_policy_ipv4_is_private() {
local ip="$1"
case "${ip}" in
"" | localhost | 127.* | 0.0.0.0 | 10.* | 192.168.* | 172.1[6-9].* | 172.2[0-9].* | 172.3[0-1].* | 169.254.*)
return 0
;;
esac
return 1
}
mcp_policy_ipv4_from_v4mapped_hex() {
# Convert IPv4-mapped IPv6 in hex form to dotted IPv4.
# Examples:
# ::ffff:7f00:1 -> 127.0.0.1
# 0:0:0:0:0:ffff:0a00:0001 -> 10.0.0.1
local ip="$1"
ip="$(printf '%s' "${ip}" | tr '[:upper:]' '[:lower:]')"
# Strip brackets and zone IDs.
if [ "${ip#\[}" != "${ip}" ]; then
ip="${ip#[}"
ip="${ip%]}"
fi
ip="${ip%%%*}"
case "${ip}" in
*":ffff:"*) ;;
*)
return 1
;;
esac
# Use the last ":ffff:" segment (handles full forms with multiple hextets).
local tail="${ip##*:ffff:}"
# Must be two hextets separated by ":" (some stacks may omit leading zeros).
case "${tail}" in
*:*) ;;
*) return 1 ;;
esac
local hi="${tail%%:*}"
local lo="${tail#*:}"
[ -n "${hi}" ] && [ -n "${lo}" ] || return 1
# Ensure hex-only hextets up to 4 digits.
if ! printf '%s' "${hi}" | grep -Eq '^[0-9a-f]{1,4}$'; then
return 1
fi
if ! printf '%s' "${lo}" | grep -Eq '^[0-9a-f]{1,4}$'; then
return 1
fi
local hi_val lo_val
hi_val=$((16#${hi}))
lo_val=$((16#${lo}))
local a b c d
a=$(((hi_val >> 8) & 255))
b=$((hi_val & 255))
c=$(((lo_val >> 8) & 255))
d=$((lo_val & 255))
printf '%s.%s.%s.%s' "${a}" "${b}" "${c}" "${d}"
}
mcp_policy_ip_is_private() {
local ip="$1"
# Normalize for matching: strip brackets and zone IDs, and lowercase.
if [ "${ip#\[}" != "${ip}" ]; then
ip="${ip#[}"
ip="${ip%]}"
fi
ip="${ip%%%*}"
ip="$(printf '%s' "${ip}" | tr '[:upper:]' '[:lower:]')"
case "${ip}" in
"" | localhost)
return 0
;;
esac
if mcp_policy_ipv4_is_private "${ip}"; then
return 0
fi
case "${ip}" in
::1 | "[::1]" | fe80:* | fc??:* | fd??:*)
return 0
;;
::ffff:127.* | ::ffff:10.* | ::ffff:192.168.* | ::ffff:172.1[6-9].* | ::ffff:172.2[0-9].* | ::ffff:172.3[0-1].* | ::ffff:169.254.*)
return 0
;;
::ffff:0:0:127.* | ::ffff:0:0:10.* | ::ffff:0:0:192.168.* | ::ffff:0:0:172.1[6-9].* | ::ffff:0:0:172.2[0-9].* | ::ffff:0:0:172.3[0-1].* | ::ffff:0:0:169.254.*)
return 0
;;
esac
# Catch IPv4-mapped IPv6 in hex hextet form (e.g., ::ffff:7f00:1).
local mapped_v4=""
mapped_v4="$(mcp_policy_ipv4_from_v4mapped_hex "${ip}" 2>/dev/null || true)"
if [ -n "${mapped_v4}" ] && mcp_policy_ipv4_is_private "${mapped_v4}"; then
return 0
fi
return 1
}
mcp_policy_normalize_host() {
local host="$1"
if [ -z "${host}" ]; then
return 1
fi
if [ "${host#\[}" != "${host}" ]; then
host="${host#[}"
host="${host%]}"
fi
printf '%s' "${host}" | tr '[:upper:]' '[:lower:]'
}
mcp_policy_extract_host_from_url() {
local url="$1"
# Parse the authority portion of a URL safely enough for SSRF defense:
# - Strip path/query/fragment
# - Strip userinfo (user:pass@) which is otherwise a bypass vector
# - Support bracketed IPv6 literals with optional port
local authority="${url#*://}"
authority="${authority%%/*}"
authority="${authority%%\?*}"
authority="${authority%%\#*}"
# If userinfo is present, keep only the host[:port] portion.
authority="${authority##*@}"
local host=""
case "${authority}" in
\[*\]*)
# [ipv6]:port or [ipv6]
host="${authority#\[}"
host="${host%%\]*}"
;;
*)
host="${authority%%:*}"
;;
esac
mcp_policy_normalize_host "${host}"
}
mcp_policy_resolve_ips() {
local host="$1"
local resolved=""
if command -v getent >/dev/null 2>&1; then
resolved="$(getent ahosts "${host}" 2>/dev/null | awk '{print $1}')"
fi
if [ -z "${resolved}" ] && command -v dig >/dev/null 2>&1; then
resolved="$(dig +short "${host}" A AAAA 2>/dev/null | sed '/^$/d')"
fi
if [ -z "${resolved}" ] && command -v host >/dev/null 2>&1; then
resolved="$(host "${host}" 2>/dev/null | awk '/has address/{print $4}/IPv6 address/{print $5}')"
fi
if [ -z "${resolved}" ] && command -v nslookup >/dev/null 2>&1; then
resolved="$(nslookup "${host}" 2>/dev/null | awk '/^Address: /{print $2}' | tail -n +2)"
fi
resolved="$(printf '%s\n' "${resolved}" | sed '/^$/d' | sort -u)"
if [ -z "${resolved}" ]; then
return 1
fi
printf '%s\n' "${resolved}"
}
mcp_policy_host_is_private() {
local host="$1"
local resolved_ips
if mcp_policy_ip_is_private "${host}"; then
return 0
fi
if resolved_ips="$(mcp_policy_resolve_ips "${host}")"; then
while IFS= read -r ip; do
[ -z "${ip}" ] && continue
ip="$(printf '%s' "${ip}" | tr '[:upper:]' '[:lower:]')"
if mcp_policy_ip_is_private "${ip}"; then
return 0
fi
done <<EOF
${resolved_ips}
EOF
fi
return 1
}
mcp_policy_host_match_list() {
local host="$1"
local list="$2"
local token
list="${list//,/ }"
for token in ${list}; do
[ -z "${token}" ] && continue
if [ "${host}" = "$(mcp_policy_normalize_host "${token}")" ]; then
return 0
fi
done
return 1
}
mcp_policy_host_allowed() {
local host="$1"
local allow_list="$2"
local deny_list="$3"
if [ -n "${deny_list}" ] && mcp_policy_host_match_list "${host}" "${deny_list}"; then
return 1
fi
if [ -n "${allow_list}" ]; then
if mcp_policy_host_match_list "${host}" "${allow_list}"; then
return 0
fi
return 1
fi
return 0
}
