[release-branch.go1.24] crypto/x509: properly check for IPv6 hosts in URIs

When checking URI constraints, use netip.ParseAddr, which understands
zones, unlike net.ParseIP which chokes on them. This prevents zone IDs
from mistakenly satisfying URI constraints.

Thanks to Juho Forsén of Mattermost for reporting this issue.

For #71156
Fixes #71209
Fixes CVE-2024-45341

Change-Id: Iecac2529f3605382d257996e0fb6d6983547e400
Reviewed-on: https://go-internal-review.googlesource.com/c/go/+/1700
Reviewed-by: Tatiana Bradley <tatianabradley@google.com>
Reviewed-by: Damien Neil <dneil@google.com>
(cherry picked from commit 22ca55d396ba801e6ae9b2bd67a059fcb30562fd)
Reviewed-on: https://go-internal-review.googlesource.com/c/go/+/1800
Commit-Queue: Roland Shoemaker <bracewell@google.com>
Reviewed-by: Roland Shoemaker <bracewell@google.com>
Reviewed-on: https://go-review.googlesource.com/c/go/+/643099
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Auto-Submit: Michael Knyszek <mknyszek@google.com>
Reviewed-by: Michael Pratt <mpratt@google.com>

src/crypto/x509/name_constraints_test.go

@@ -1607,6 +1607,23 @@ var nameConstraintsTests = []nameConstraintsTest{
 		leaf:          leafSpec{sans: []string{"dns:.example.com"}},
 		expectedError: "cannot parse dnsName \".example.com\"",
 	},
+	// #86: URIs with IPv6 addresses with zones and ports are rejected
+	{
+		roots: []constraintsSpec{
+			{
+				ok: []string{"uri:example.com"},
+			},
+		},
+		intermediates: [][]constraintsSpec{
+			{
+				{},
+			},
+		},
+		leaf: leafSpec{
+			sans: []string{"uri:http://[2006:abcd::1%25.example.com]:16/"},
+		},
+		expectedError: "URI with IP",
+	},
 }
 
 func makeConstraintsCACert(constraints constraintsSpec, name string, key *ecdsa.PrivateKey, parent *Certificate, parentKey *ecdsa.PrivateKey) (*Certificate, error) {

src/crypto/x509/verify.go

@@ -13,6 +13,7 @@ import (
 	"iter"
 	"maps"
 	"net"
+	"net/netip"
 	"net/url"
 	"reflect"
 	"runtime"
@@ -465,8 +466,10 @@ func matchURIConstraint(uri *url.URL, constraint string) (bool, error) {
 		}
 	}
 
-	if strings.HasPrefix(host, "[") && strings.HasSuffix(host, "]") ||
+	// netip.ParseAddr will reject the URI IPv6 literal form "[...]", so we
-		net.ParseIP(host) != nil {
+	// check if _either_ the string parses as an IP, or if it is enclosed in
+	// square brackets.
+	if _, err := netip.ParseAddr(host); err == nil || (strings.HasPrefix(host, "[") && strings.HasSuffix(host, "]")) {
 		return false, fmt.Errorf("URI with IP (%q) cannot be matched against constraints", uri.String())
 	}