net/http, net/http/cookiejar: avoid subdomain matches on IPv6 zones

When deciding whether to forward cookies or sensitive headers
across a redirect, do not attempt to interpret an IPv6 address
as a domain name.

Avoids a case where a maliciously-crafted redirect to an
IPv6 address with a scoped addressing zone could be
misinterpreted as a within-domain redirect. For example,
we could interpret "::1%.www.example.com" as a subdomain
of "www.example.com".

Thanks to Juho Nurminen of Mattermost for reporting this issue.

Fixes CVE-2023-45289
Fixes #65065

Change-Id: I8f463f59f0e700c8a18733d2b264a8bcb3a19599
Reviewed-on: https://team-review.git.corp.google.com/c/golang/go-private/+/2131938
Reviewed-by: Tatiana Bradley <tatianabradley@google.com>
Reviewed-by: Roland Shoemaker <bracewell@google.com>
Reviewed-on: https://go-review.googlesource.com/c/go/+/569340
Reviewed-by: Damien Neil <dneil@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Carlos Amedee <carlos@golang.org>
Auto-Submit: Michael Knyszek <mknyszek@google.com>

src/net/http/client.go

@@ -1008,6 +1008,12 @@ func isDomainOrSubdomain(sub, parent string) bool {
 	if sub == parent {
 		return true
 	}
+	// If sub contains a :, it's probably an IPv6 address (and is definitely not a hostname).
+	// Don't check the suffix in this case, to avoid matching the contents of a IPv6 zone.
+	// For example, "::1%.www.example.com" is not a subdomain of "www.example.com".
+	if strings.ContainsAny(sub, ":%") {
+		return false
+	}
 	// If sub is "foo.example.com" and parent is "example.com",
 	// that means sub must end in "."+parent.
 	// Do it without allocating.

src/net/http/client_test.go

@@ -1717,6 +1717,7 @@ func TestShouldCopyHeaderOnRedirect(t *testing.T) {
 		{"authorization", "http://foo.com/", "https://foo.com/", true},
 		{"authorization", "http://foo.com:1234/", "http://foo.com:4321/", true},
 		{"www-authenticate", "http://foo.com/", "http://bar.com/", false},
+		{"authorization", "http://foo.com/", "http://[::1%25.foo.com]/", false},
 
 		// But subdomains should work:
 		{"www-authenticate", "http://foo.com/", "http://foo.com/", true},

src/net/http/cookiejar/jar.go

@@ -362,6 +362,13 @@ func jarKey(host string, psl PublicSuffixList) string {
 
 // isIP reports whether host is an IP address.
 func isIP(host string) bool {
+	if strings.ContainsAny(host, ":%") {
+		// Probable IPv6 address.
+		// Hostnames can't contain : or %, so this is definitely not a valid host.
+		// Treating it as an IP is the more conservative option, and avoids the risk
+		// of interpeting ::1%.www.example.com as a subtomain of www.example.com.
+		return true
+	}
 	return net.ParseIP(host) != nil
 }
 

src/net/http/cookiejar/jar_test.go

@@ -252,6 +252,7 @@ var isIPTests = map[string]bool{
 	"127.0.0.1":            true,
 	"1.2.3.4":              true,
 	"2001:4860:0:2001::68": true,
+	"::1%zone":             true,
 	"example.com":          false,
 	"1.1.1.300":            false,
 	"www.foo.bar.net":      false,
@@ -629,6 +630,15 @@ var basicsTests = [...]jarTest{
 			{"http://www.host.test:1234/", "a=1"},
 		},
 	},
+	{
+		"IPv6 zone is not treated as a host.",
+		"https://example.com/",
+		[]string{"a=1"},
+		"a=1",
+		[]query{
+			{"https://[::1%25.example.com]:80/", ""},
+		},
+	},
 }
 
 func TestBasics(t *testing.T) {