Harden IPv6 validation

lib/common.sh

@@ -247,13 +247,42 @@ validate_ipv4() {
   done
 }
 
+_validate_ipv6_part_count() {
+  local part=${1-}
+  local IFS=':'
+  local -a fields=()
+  local field idx count=0
+
+  [[ -n ${part} ]] || {
+    printf '0\n'
+    return 0
+  }
+
+  [[ ${part} != :* ]] || return 1
+  [[ ${part} != *: ]] || return 1
+  [[ ${part} != *::* ]] || return 1
+
+  read -r -a fields <<<"${part}"
+  for idx in "${!fields[@]}"; do
+    field=${fields[idx]}
+    [[ -n ${field} ]] || return 1
+    if [[ ${field} == IPV4TAIL ]]; then
+      (( idx == ${#fields[@]} - 1 )) || return 1
+      ((count += 2))
+      continue
+    fi
+    [[ ${field} =~ ^[0-9A-Fa-f]{1,4}$ ]] || return 1
+    ((count++))
+  done
+
+  printf '%s\n' "${count}"
+}
+
 validate_ipv6() {
   local ip=${1-}
-  local base scope
+  local base scope tail prefix left right left_count right_count total_count
   [[ -n ${ip} ]] || return 1
-  [[ ${ip} != *.* ]] || return 1
   [[ ${ip} == *:* ]] || return 1
-  [[ ${ip} != *:::* ]] || return 1
 
   scope=''
   base=${ip}
@@ -264,8 +293,29 @@ validate_ipv6() {
     [[ ${scope} =~ ^[A-Za-z0-9_.:-]+$ ]] || return 1
   fi
 
-  [[ ${base} =~ ^[0-9A-Fa-f:]+$ ]] || return 1
-  [[ ${base} =~ :: ]] || [[ ${base} =~ ^([0-9A-Fa-f]{1,4}:){1,7}[0-9A-Fa-f]{1,4}$ ]] || return 1
+  if [[ ${base} == *.* ]]; then
+    tail=${base##*:}
+    prefix=${base%:*}
+    [[ ${prefix} != "${base}" ]] || return 1
+    validate_ipv4 "${tail}" || return 1
+    base="${prefix}:IPV4TAIL"
+  fi
+
+  [[ ${base//IPV4TAIL/} =~ ^[0-9A-Fa-f:]+$ ]] || return 1
+
+  if [[ ${base} == *::* ]]; then
+    [[ ${base#*::} != *::* ]] || return 1
+    left=${base%%::*}
+    right=${base#*::}
+    left_count=$(_validate_ipv6_part_count "${left}") || return 1
+    right_count=$(_validate_ipv6_part_count "${right}") || return 1
+    total_count=$((left_count + right_count))
+    (( total_count < 8 )) || return 1
+    return 0
+  fi
+
+  total_count=$(_validate_ipv6_part_count "${base}") || return 1
+  (( total_count == 8 ))
 }
 
 validate_port() {

tests/test_common.sh

@@ -26,7 +26,11 @@ assert_status 1 "$(status_of validate_ipv4 '')" 'validate_ipv4 should reject emp
 assert_status 0 "$(status_of validate_ipv6 '::1')" 'validate_ipv6 should accept loopback'
 assert_status 0 "$(status_of validate_ipv6 '2001:db8::1')" 'validate_ipv6 should accept compressed address'
 assert_status 0 "$(status_of validate_ipv6 'fe80::1%eth0')" 'validate_ipv6 should accept scoped address'
+assert_status 0 "$(status_of validate_ipv6 '::ffff:192.0.2.128')" 'validate_ipv6 should accept embedded ipv4 tail'
 assert_status 1 "$(status_of validate_ipv6 ':::1')" 'validate_ipv6 should reject malformed address'
+assert_status 1 "$(status_of validate_ipv6 '2001::1::1')" 'validate_ipv6 should reject multiple compression markers'
+assert_status 1 "$(status_of validate_ipv6 '12345::1')" 'validate_ipv6 should reject oversized hextet'
+assert_status 1 "$(status_of validate_ipv6 '2001:db8::1::')" 'validate_ipv6 should reject trailing double compression'
 assert_status 1 "$(status_of validate_ipv6 '1.2.3.4')" 'validate_ipv6 should reject ipv4 literal'
 assert_status 1 "$(status_of validate_ipv6 '')" 'validate_ipv6 should reject empty string'