diff --git a/supabase/functions/_backend/utils/ip.ts b/supabase/functions/_backend/utils/ip.ts
new file mode 100644
index 0000000000..a07b0c66ea
--- /dev/null
+++ b/supabase/functions/_backend/utils/ip.ts
@@ -0,0 +1,125 @@
+export function isPrivateIpv4(ip: string) {
+  if (!/^\d{1,3}(?:\.\d{1,3}){3}$/.test(ip)) {
+    return true
+  }
+
+  const octets = ip.split('.').map(part => Number.parseInt(part, 10))
+  if (octets.some(part => Number.isNaN(part) || part < 0 || part > 255)) {
+    return true
+  }
+
+  const [a, b, c] = octets
+  return a === 0
+    || a === 10
+    || a === 127
+    || (a === 169 && b === 254)
+    || (a === 172 && b >= 16 && b <= 31)
+    || (a === 192 && b === 168)
+    || (a === 100 && b >= 64 && b <= 127)
+    || (a === 198 && (b === 18 || b === 19))
+    || (a === 192 && b === 88 && octets[2] === 99)
+    || a >= 224
+    // Reserved TEST-NET ranges are also non-public for server-side fetch paths.
+    || (a === 192 && b === 0 && c === 0)
+    || (a === 192 && b === 0 && octets[2] === 2)
+    || (a === 198 && b === 51 && octets[2] === 100)
+    || (a === 203 && b === 0 && octets[2] === 113)
+}
+
+export function isPrivateIpv6(ip: string) {
+  const normalized = ip.toLowerCase()
+  if (normalized === '::1' || normalized === '::') {
+    return true
+  }
+  if (normalized.startsWith('::ffff:')) {
+    const mappedIpv4 = normalizeMappedIpv4(normalized.slice(7))
+    return isPrivateIpv4(mappedIpv4)
+  }
+
+  const hextets = parseIpv6Hextets(normalized)
+  if (!hextets) {
+    return true
+  }
+
+  const [firstHextet, secondHextet] = hextets
+  if (
+    (firstHextet & 0xFFC0) === 0xFE80
+    || (firstHextet & 0xFFC0) === 0xFEC0
+    || (firstHextet & 0xFE00) === 0xFC00
+    || (firstHextet & 0xFF00) === 0xFF00
+    || firstHextet === 0x2002
+    || (firstHextet === 0x2001 && secondHextet === 0x0DB8)
+    || (firstHextet === 0x2001 && secondHextet === 0x0002)
+    || (firstHextet === 0x2001 && (secondHextet & 0xFFF0) === 0x0010)
+  ) {
+    return true
+  }
+  return false
+}
+
+export function isPrivateIp(ip: string) {
+  return ip.includes(':') ? isPrivateIpv6(ip) : isPrivateIpv4(ip)
+}
+
+function normalizeMappedIpv4(value: string) {
+  if (value.includes('.')) {
+    return value
+  }
+
+  const parts = value.split(':')
+  if (parts.length !== 2) {
+    return value
+  }
+
+  const [high, low] = parts.map(part => Number.parseInt(part, 16))
+  if (
+    !Number.isFinite(high)
+    || !Number.isFinite(low)
+    || high < 0
+    || high > 0xFFFF
+    || low < 0
+    || low > 0xFFFF
+  ) {
+    return value
+  }
+
+  return [
+    high >> 8,
+    high & 0xFF,
+    low >> 8,
+    low & 0xFF,
+  ].join('.')
+}
+
+function parseIpv6Hextets(value: string) {
+  if (value.includes('.')) {
+    return null
+  }
+
+  const compressed = value.split('::')
+  if (compressed.length > 2) {
+    return null
+  }
+
+  const [left, right = ''] = compressed
+  const leftParts = left ? left.split(':') : []
+  const rightParts = right ? right.split(':') : []
+  const explicitParts = [...leftParts, ...rightParts]
+  if (explicitParts.some(part => !/^[\da-f]{1,4}$/.test(part))) {
+    return null
+  }
+
+  const missingCount = 8 - explicitParts.length
+  if (compressed.length === 1 && missingCount !== 0) {
+    return null
+  }
+  if (compressed.length === 2 && missingCount < 1) {
+    return null
+  }
+
+  return [
+    ...leftParts,
+    ...(Array.from({ length: compressed.length === 2 ? missingCount : 0 }).fill('0') as string[]),
+    ...rightParts,
+  ].map(part => Number.parseInt(part, 16))
+}
diff --git a/supabase/functions/_backend/utils/publicUrl.ts b/supabase/functions/_backend/utils/publicUrl.ts
index 34a3de90aa..6417c362dd 100644
--- a/supabase/functions/_backend/utils/publicUrl.ts
+++ b/supabase/functions/_backend/utils/publicUrl.ts
@@ -1,3 +1,5 @@
+import { isPrivateIp } from './ip.ts'
+
 const DNS_LOOKUP_URL = 'https://cloudflare-dns.com/dns-query'
 const DNS_LOOKUP_TIMEOUT_MS = 1500
 const DEFAULT_MAX_REDIRECTS = 5
@@ -37,49 +39,6 @@ function isIpLiteral(hostname: string): boolean {
   return IPV4_REGEX.test(hostname) || hostname.includes(':')
 }
 
-function isPrivateIpv4(ip: string) {
-  const octets = ip.split('.').map(part => Number.parseInt(part, 10))
-  if (octets.length !== 4 || octets.some(part => Number.isNaN(part) || part < 0 || part > 255))
-    return true
-
-  const [a, b, c] = octets
-  return a === 0
-    || a === 10
-    || a === 127
-    || (a === 100 && b >= 64 && b <= 127)
-    || (a === 169 && b === 254)
-    || (a === 172 && b >= 16 && b <= 31)
-    || (a === 192 && b === 0 && c === 0)
-    || (a === 192 && b === 0 && c === 2)
-    || (a === 192 && b === 88 && c === 99)
-    || (a === 192 && b === 168)
-    || (a === 198 && (b === 18 || b === 19))
-    || (a === 198 && b === 51 && c === 100)
-    || (a === 203 && b === 0 && c === 113)
-    || a >= 224
-}
-
-function isPrivateIpv6(ip: string) {
-  const normalized = ip.toLowerCase()
-
-  if (normalized === '::' || normalized === '::1')
-    return true
-  if (normalized.startsWith('::ffff:'))
-    return isPrivateIpv4(normalized.slice(7))
-  if (normalized.startsWith('100:') || normalized.startsWith('2001:db8:') || normalized.startsWith('2002:'))
-    return true
-  if (normalized.startsWith('fc') || normalized.startsWith('fd') || normalized.startsWith('fe8') || normalized.startsWith('fe9') || normalized.startsWith('fea') || normalized.startsWith('feb'))
-    return true
-  if (normalized.startsWith('ff'))
-    return true
-
-  return false
-}
-
-function isPrivateIp(ip: string) {
-  return ip.includes(':') ? isPrivateIpv6(ip) : isPrivateIpv4(ip)
-}
-
 async function resolveHostnameIps(hostname: string, type: 'A' | 'AAAA') {
   const controller = new AbortController()
   const timeoutId = setTimeout(() => controller.abort(), DNS_LOOKUP_TIMEOUT_MS)
diff --git a/tests/website-preview-security.unit.test.ts b/tests/website-preview-security.unit.test.ts
new file mode 100644
index 0000000000..50d355010c
--- /dev/null
+++ b/tests/website-preview-security.unit.test.ts
@@ -0,0 +1,54 @@
+import { describe, expect, it } from 'vitest'
+import { isPrivateIp } from '../supabase/functions/_backend/utils/ip.ts'
+
+describe('website preview IP validation', () => {
+  it('rejects non-public IPv4 ranges returned by DNS', () => {
+    expect(isPrivateIp('10.0.0.1')).toBe(true)
+    expect(isPrivateIp('127.0.0.1')).toBe(true)
+    expect(isPrivateIp('169.254.169.254')).toBe(true)
+    expect(isPrivateIp('172.16.0.1')).toBe(true)
+    expect(isPrivateIp('192.168.1.1')).toBe(true)
+    expect(isPrivateIp('100.64.0.1')).toBe(true)
+    expect(isPrivateIp('198.18.0.1')).toBe(true)
+    expect(isPrivateIp('192.0.2.1')).toBe(true)
+    expect(isPrivateIp('198.51.100.1')).toBe(true)
+    expect(isPrivateIp('203.0.113.1')).toBe(true)
+    expect(isPrivateIp('192.88.99.1')).toBe(true)
+    expect(isPrivateIp('224.0.0.1')).toBe(true)
+    expect(isPrivateIp('240.0.0.1')).toBe(true)
+    expect(isPrivateIp('255.255.255.255')).toBe(true)
+    expect(isPrivateIp('1.2.3.foo')).toBe(true)
+    expect(isPrivateIp('192.0.1.1')).toBe(false)
+  })
+
+  it('rejects non-public IPv6 ranges returned by DNS', () => {
+    expect(isPrivateIp('::')).toBe(true)
+    expect(isPrivateIp('::1')).toBe(true)
+    expect(isPrivateIp('fe80::1')).toBe(true)
+    expect(isPrivateIp('fe90::1')).toBe(true)
+    expect(isPrivateIp('febf::1')).toBe(true)
+    expect(isPrivateIp('fec0::1')).toBe(true)
+    expect(isPrivateIp('feff::1')).toBe(true)
+    expect(isPrivateIp('fc00::1')).toBe(true)
+    expect(isPrivateIp('fd00::1')).toBe(true)
+    expect(isPrivateIp('ff02::1')).toBe(true)
+    expect(isPrivateIp('2001:db8::1')).toBe(true)
+    expect(isPrivateIp('2001:0db8::1')).toBe(true)
+    expect(isPrivateIp('2001:2::1')).toBe(true)
+    expect(isPrivateIp('2001:0002::1')).toBe(true)
+    expect(isPrivateIp('2001:10::1')).toBe(true)
+    expect(isPrivateIp('2001:1f::1')).toBe(true)
+    expect(isPrivateIp('2002::1')).toBe(true)
+    expect(isPrivateIp('::ffff:127.0.0.1')).toBe(true)
+    expect(isPrivateIp('::ffff:7f00:1')).toBe(true)
+    expect(isPrivateIp('abcd:foo')).toBe(true)
+    expect(isPrivateIp('2001:::1')).toBe(true)
+  })
+
+  it('allows globally routable DNS answers', () => {
+    expect(isPrivateIp('8.8.8.8')).toBe(false)
+    expect(isPrivateIp('1.1.1.1')).toBe(false)
+    expect(isPrivateIp('2606:4700:4700::1111')).toBe(false)
+    expect(isPrivateIp('2001:4860:4860::8888')).toBe(false)
+  })
+})