Validate IPv6 addresses in urls

ipv6.go

@@ -0,0 +1,195 @@
+package fasthttp
+
+import (
+	"bytes"
+	"errors"
+)
+
+var (
+	errInvalidIPv6Host    = errors.New("invalid IPv6 host")
+	errInvalidIPv6Zone    = errors.New("invalid IPv6 zone")
+	errInvalidIPv6Address = errors.New("invalid IPv6 address")
+)
+
+func validateIPv6Literal(host []byte) error {
+	if len(host) == 0 || host[0] != '[' {
+		return nil
+	}
+	end := bytes.IndexByte(host, ']')
+	if end < 0 || end == 1 {
+		return errInvalidIPv6Host
+	}
+	addr := host[1:end]
+
+	// Optional zone.
+	if zi := bytes.IndexByte(addr, '%'); zi >= 0 {
+		if zi == len(addr)-1 {
+			return errInvalidIPv6Zone
+		}
+		addr = addr[:zi]
+	}
+
+	// Must have a colon to be IPv6.
+	if bytes.IndexByte(addr, ':') < 0 {
+		return errInvalidIPv6Address
+	}
+
+	// IPv4-embedded?
+	if bytes.IndexByte(addr, '.') >= 0 {
+		lastColon := bytes.LastIndexByte(addr, ':')
+		if lastColon < 0 || lastColon == len(addr)-1 {
+			return errInvalidIPv6Address
+		}
+
+		ipv4 := addr[lastColon+1:]
+		if !validIPv4(ipv4) {
+			return errInvalidIPv6Address
+		}
+
+		head := addr[:lastColon]
+		seenDoubleAtSplit := lastColon > 0 && addr[lastColon-1] == ':'
+		if seenDoubleAtSplit {
+			head = addr[:lastColon-1]
+		}
+
+		hextets, seenDoubleHead, ok := parseIPv6Hextets(head, false)
+		if !ok {
+			return errInvalidIPv6Address
+		}
+
+		if seenDoubleHead && seenDoubleAtSplit {
+			return errInvalidIPv6Address
+		}
+
+		hextets += 2 // IPv4 tail = 2 hextets
+		seenDouble := seenDoubleHead || seenDoubleAtSplit
+
+		// '::' must compress at least one hextet.
+		if (!seenDouble && hextets != 8) || (seenDouble && hextets >= 8) {
+			return errInvalidIPv6Address
+		}
+		return nil
+	}
+
+	// Pure IPv6
+	hextets, seenDouble, ok := parseIPv6Hextets(addr, false)
+	if !ok {
+		return errInvalidIPv6Address
+	}
+	if (!seenDouble && hextets != 8) || (seenDouble && hextets >= 8) {
+		return errInvalidIPv6Address
+	}
+	return nil
+}
+
+func parseIPv6Hextets(s []byte, allowTrailingColon bool) (groups int, seenDouble, ok bool) {
+	n := len(s)
+	if n == 0 {
+		return 0, false, true
+	}
+	i := 0
+	justSawDouble := false
+
+	for i < n {
+		if s[i] == ':' {
+			if i+1 < n && s[i+1] == ':' {
+				if seenDouble || justSawDouble {
+					return 0, false, false
+				}
+				seenDouble = true
+				justSawDouble = true
+				i += 2
+				if i == n {
+					break
+				}
+				continue
+			}
+			if i == 0 {
+				return 0, false, false
+			}
+			if justSawDouble {
+				return 0, false, false
+			}
+			if i == n-1 {
+				if allowTrailingColon {
+					break
+				}
+				return 0, false, false
+			}
+			if !ishex(s[i+1]) {
+				return 0, false, false
+			}
+			i++
+			continue
+		}
+
+		justSawDouble = false
+		cnt := 0
+		for cnt < 4 && i < n && ishex(s[i]) {
+			i++
+			cnt++
+		}
+		if cnt == 0 {
+			return 0, false, false
+		}
+		groups++
+
+		if i < n && s[i] != ':' {
+			return 0, false, false
+		}
+	}
+	return groups, seenDouble, true
+}
+
+// validIPv4 validates a dotted-quad (exactly 4 parts, 0..255) with no leading zeros
+// unless the octet is exactly "0".
+func validIPv4(s []byte) bool {
+	parts := 0
+	i := 0
+	n := len(s)
+
+	for parts < 4 {
+		if i >= n {
+			return false
+		}
+
+		start := i
+		val := 0
+		digits := 0
+
+		for i < n {
+			c := s[i]
+			if c < '0' || c > '9' {
+				break
+			}
+			val = val*10 + int(c-'0')
+			if val > 255 {
+				return false
+			}
+			i++
+			digits++
+			if digits > 3 {
+				return false
+			}
+		}
+		if digits == 0 {
+			return false
+		}
+
+		// Disallow leading zeros like "00", "01", "001".
+		// Allowed: exactly "0" or any number that doesn't start with '0'.
+		if digits > 1 && s[start] == '0' {
+			return false
+		}
+
+		parts++
+		if parts == 4 {
+			return i == n // must consume all input
+		}
+		if i >= n || s[i] != '.' {
+			return false
+		}
+		i++ // skip dot
+	}
+	return false
+}

ipv6_test.go

@@ -0,0 +1,85 @@
+package fasthttp
+
+import (
+	"bytes"
+	"net"
+	"testing"
+)
+
+// oracleValid replicates the original function's semantics using net.ParseIP:
+// - Input must start with '['
+// - There must be a closing ']' and a non-empty address between
+// - Optional %zone allowed but must not be empty
+// - Zone is stripped before checking with net.ParseIP
+// - Must contain a ':' to be IPv6 (prevents raw IPv4-in-brackets).
+func oracleValid(host []byte) bool {
+	if len(host) == 0 || host[0] != '[' {
+		// Original function: non-bracketed hosts return nil (treated as valid/no-op).
+		return true
+	}
+
+	end := bytes.IndexByte(host, ']')
+	if end < 0 {
+		return false
+	}
+	addr := host[1:end]
+	if len(addr) == 0 {
+		return false
+	}
+
+	// Split off %zone (if present).
+	if zi := bytes.IndexByte(addr, '%'); zi >= 0 {
+		// Zone must not be empty.
+		if zi == len(addr)-1 {
+			return false
+		}
+		addr = addr[:zi]
+	}
+
+	// Must contain ':' to be IPv6.
+	if bytes.IndexByte(addr, ':') < 0 {
+		return false
+	}
+
+	// Use net.ParseIP on the de-zoned address (this was the original check).
+	if ip := net.ParseIP(string(addr)); ip == nil {
+		return false
+	}
+	return true
+}
+
+func FuzzValidateIPv6Literal(f *testing.F) {
+	seeds := [][]byte{
+		[]byte(""),            // non-bracketed => valid (no-op)
+		[]byte("example.com"), // non-bracketed => valid (no-op)
+		[]byte("["),           // unterminated
+		[]byte("[]"),          // empty
+		[]byte("[::]"),
+		[]byte("[::1]"),
+		[]byte("[2001:db8::1]"),
+		[]byte("[2001:db8::]"),
+		[]byte("[::ffff:192.168.0.1]"),
+		[]byte("[fe80::1%eth0]"),
+		[]byte("[fe80::1%]"),         // empty zone
+		[]byte("[1234]"),             // no colon
+		[]byte("[2001:db8:zzzz::1]"), // invalid hex
+		[]byte("[::ffff:256.0.0.1]"), // invalid v4 tail
+		[]byte("[2001:db8:::1]"),     // triple colon
+		[]byte("[::1]:443"),          // trailing port outside ']' is ignored by validator
+		[]byte("[2001:db8:0:0:0:0:2:1]"),
+		[]byte("[2001:db8:0:0:0:0:2:1%en0]"),
+	}
+	for _, s := range seeds {
+		f.Add(s)
+	}
+
+	f.Fuzz(func(t *testing.T, host []byte) {
+		gotErr := validateIPv6Literal(host)
+		wantValid := oracleValid(host)
+
+		if (gotErr == nil) != wantValid {
+			t.Fatalf("mismatch for %q: validateIPv6Literal err=%v, oracleValid=%v",
+				b2s(host), gotErr, wantValid)
+		}
+	})
+}

uri.go

@@ -408,6 +408,9 @@ func parseHost(host []byte) ([]byte, error) {
 	if host, err = unescape(host, encodeHost); err != nil {
 		return nil, err
 	}
+	if err = validateIPv6Literal(host); err != nil {
+		return nil, err
+	}
 	return host, nil
 }
 

uri_test.go

@@ -104,6 +104,33 @@ func testURIPathEscape(t *testing.T, path, expectedRequestURI string) {
 	}
 }
 
+func TestURIRejectInvalidIPv6(t *testing.T) {
+	t.Parallel()
+
+	for _, raw := range []string{
+		"http://[0:0::vulndetector.com]:80",
+		"http://[2001:db8::vulndetector.com]/",
+		"http://[vulndetector.com]/",
+		"http://[::ffff:192.0.2.300]/",
+	} {
+		var u URI
+		if err := u.Parse(nil, []byte(raw)); err == nil {
+			t.Errorf("expected Parse to fail for %q", raw)
+		}
+	}
+
+	for _, raw := range []string{
+		"http://[2001:db8::1]/",
+		"http://[fe80::1%25en0]/",
+		"http://[::ffff:192.0.2.1]/",
+	} {
+		var u URI
+		if err := u.Parse(nil, []byte(raw)); err != nil {
+			t.Errorf("unexpected error for %q: %v", raw, err)
+		}
+	}
+}
+
 func TestURIUpdate(t *testing.T) {
 	t.Parallel()