fix(socks5): encode embedded IPv4 tails in IPv6 literals correctly (#5099)

trivikr · web-flow · commit d76f932def33 · 2026-04-24T00:52:40.000-07:00
Assisted-by: openai:gpt-5.4

Signed-off-by: Kamat, Trivikram &lt;16024985+trivikr@users.noreply.github.com&gt;
diff --git a/lib/core/socks5-utils.js b/lib/core/socks5-utils.js
@@ -46,12 +46,26 @@ function parseAddress (address) {
  */
 function parseIPv6 (address) {
   const buffer = Buffer.alloc(16)
+  let normalizedAddress = address
+
+  // Expand an embedded IPv4 tail into the last two IPv6 groups.
+  if (address.includes('.')) {
+    const lastColonIndex = address.lastIndexOf(':')
+    const ipv4Part = address.slice(lastColonIndex + 1)
+
+    if (net.isIPv4(ipv4Part)) {
+      const octets = ipv4Part.split('.').map(Number)
+      const high = ((octets[0] << 8) | octets[1]).toString(16)
+      const low = ((octets[2] << 8) | octets[3]).toString(16)
+      normalizedAddress = `${address.slice(0, lastColonIndex)}:${high}:${low}`
+    }
+  }
 
   // Handle compressed notation (::)
-  const doubleColonIndex = address.indexOf('::')
+  const doubleColonIndex = normalizedAddress.indexOf('::')
   if (doubleColonIndex !== -1) {
-    const before = address.slice(0, doubleColonIndex)
-    const after = address.slice(doubleColonIndex + 2)
+    const before = normalizedAddress.slice(0, doubleColonIndex)
+    const after = normalizedAddress.slice(doubleColonIndex + 2)
     const beforeParts = before === '' ? [] : before.split(':')
     const afterParts = after === '' ? [] : after.split(':')
 
@@ -66,7 +80,7 @@ function parseIPv6 (address) {
       bufferIndex += 2
     }
   } else {
-    const parts = address.split(':')
+    const parts = normalizedAddress.split(':')
     for (let i = 0; i < parts.length; i++) {
       buffer.writeUInt16BE(parseInt(parts[i], 16), i * 2)
     }
diff --git a/test/socks5-utils.js b/test/socks5-utils.js
@@ -48,7 +48,7 @@ test('parseAddress - Domain', async (t) => {
 })
 
 test('parseIPv6', async (t) => {
-  const p = tspl(t, { plan: 9 })
+  const p = tspl(t, { plan: 10 })
 
   // Test full IPv6
   const buffer1 = parseIPv6('2001:0db8:0000:0042:0000:8a2e:0370:7334')
@@ -74,6 +74,9 @@ test('parseIPv6', async (t) => {
   // Test trailing ::
   p.equal(parseIPv6('fe80::').toString('hex'), 'fe800000000000000000000000000000', 'should expand fe80:: correctly')
 
+  // Test IPv4-mapped IPv6
+  p.equal(parseIPv6('::ffff:192.0.2.128').toString('hex'), '00000000000000000000ffffc0000280', 'should encode embedded IPv4 tail correctly')
+
   await p.completed
 })
 
