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crypto/x509: enforce SAN IA5String encoding restrictions

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Extends the IA5String encoding restrictions that are currently applied
to name constraints to dNSName, rfc822Name, and
uniformResourceIdentifier elements of the SAN. The utility function
isIA5String is updated to use unicode.MaxASCII rather than utf8.RuneSelf
as it is somewhat more readable.

Certificates that include these badly encoded names do exist, but are
exceedingly rare. zlint and other linters enforce this encoding and
searching censys.io reveals only three currently trusted certificates
with this particular encoding issue.

Fixes #26362

Change-Id: I7a4f3e165a1754e5b4bfaeabc03e01eb7367f3c9
Reviewed-on: https://go-review.googlesource.com/c/go/+/235078
Run-TryBot: Roland Shoemaker <roland@golang.org>
TryBot-Result: Go Bot <gobot@golang.org>
Trust: Roland Shoemaker <roland@golang.org>
Reviewed-by: Filippo Valsorda <filippo@golang.org>
This commit is contained in:
Roland Shoemaker 2020-05-23 10:15:46 -07:00 committed by Roland Shoemaker
parent ae329abec0
commit 1eeaff75f9
3 changed files with 131 additions and 8 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

10
doc/go1.16.html
View File

@ -174,6 +174,16 @@ Do not send CLs removing the interior tags from such phrases.
by the <code>Error</code> method with <code>"tls: use of closed connection"</code>.
</p>
<h3 id="crypto/x509"><a href="/pkg/crypto/x509">crypto/x509</a></h3>
<p><!-- CL 235078 -->
<a href="/pkg/crypto/x509/#ParseCertificate">ParseCertificate</a> and
<a href="/pkg/crypto/x509/#CreateCertificate">CreateCertificate</a> both
now enforce string encoding restrictions for the fields <code>DNSNames</code>,
<code>EmailAddresses</code>, and <code>URIs</code>. These fields can only
contain strings with characters within the ASCII range.
</p>
<h3 id="net"><a href="/pkg/net/">net</a></h3>
<p><!-- CL 250357 -->

39
src/crypto/x509/x509.go
View File

@ -28,7 +28,7 @@ import (
"strconv"
"strings"
"time"
"unicode/utf8"
"unicode"
"golang.org/x/crypto/cryptobyte"
cryptobyte_asn1 "golang.org/x/crypto/cryptobyte/asn1"
@ -1085,17 +1085,29 @@ func parseSANExtension(value []byte) (dnsNames, emailAddresses []string, ipAddre
err = forEachSAN(value, func(tag int, data []byte) error {
switch tag {
case nameTypeEmail:
emailAddresses = append(emailAddresses, string(data))
email := string(data)
if err := isIA5String(email); err != nil {
return errors.New("x509: SAN rfc822Name is malformed")
}
emailAddresses = append(emailAddresses, email)
case nameTypeDNS:
dnsNames = append(dnsNames, string(data))
name := string(data)
if err := isIA5String(name); err != nil {
return errors.New("x509: SAN dNSName is malformed")
}
dnsNames = append(dnsNames, string(name))
case nameTypeURI:
uri, err := url.Parse(string(data))
uriStr := string(data)
if err := isIA5String(uriStr); err != nil {
return errors.New("x509: SAN uniformResourceIdentifier is malformed")
}
uri, err := url.Parse(uriStr)
if err != nil {
return fmt.Errorf("x509: cannot parse URI %q: %s", string(data), err)
return fmt.Errorf("x509: cannot parse URI %q: %s", uriStr, err)
}
if len(uri.Host) > 0 {
if _, ok := domainToReverseLabels(uri.Host); !ok {
return fmt.Errorf("x509: cannot parse URI %q: invalid domain", string(data))
return fmt.Errorf("x509: cannot parse URI %q: invalid domain", uriStr)
}
}
uris = append(uris, uri)
@ -1625,9 +1637,15 @@ func oidInExtensions(oid asn1.ObjectIdentifier, extensions []pkix.Extension) boo
func marshalSANs(dnsNames, emailAddresses []string, ipAddresses []net.IP, uris []*url.URL) (derBytes []byte, err error) {
var rawValues []asn1.RawValue
for _, name := range dnsNames {
if err := isIA5String(name); err != nil {
return nil, err
}
rawValues = append(rawValues, asn1.RawValue{Tag: nameTypeDNS, Class: 2, Bytes: []byte(name)})
}
for _, email := range emailAddresses {
if err := isIA5String(email); err != nil {
return nil, err
}
rawValues = append(rawValues, asn1.RawValue{Tag: nameTypeEmail, Class: 2, Bytes: []byte(email)})
}
for _, rawIP := range ipAddresses {
@ -1639,14 +1657,19 @@ func marshalSANs(dnsNames, emailAddresses []string, ipAddresses []net.IP, uris [
rawValues = append(rawValues, asn1.RawValue{Tag: nameTypeIP, Class: 2, Bytes: ip})
}
for _, uri := range uris {
rawValues = append(rawValues, asn1.RawValue{Tag: nameTypeURI, Class: 2, Bytes: []byte(uri.String())})
uriStr := uri.String()
if err := isIA5String(uriStr); err != nil {
return nil, err
}
rawValues = append(rawValues, asn1.RawValue{Tag: nameTypeURI, Class: 2, Bytes: []byte(uriStr)})
}
return asn1.Marshal(rawValues)
}
func isIA5String(s string) error {
for _, r := range s {
if r >= utf8.RuneSelf {
// Per RFC5280 "IA5String is limited to the set of ASCII characters"
if r > unicode.MaxASCII {
return fmt.Errorf("x509: %q cannot be encoded as an IA5String", s)
}
}

90
src/crypto/x509/x509_test.go
View File

@ -2773,3 +2773,93 @@ func TestUnknownExtKey(t *testing.T) {
t.Errorf("expected error containing %q, got %s", errorContains, err)
}
}
func TestIA5SANEnforcement(t *testing.T) {
k, err := ecdsa.GenerateKey(elliptic.P256(), rand.Reader)
if err != nil {
t.Fatalf("ecdsa.GenerateKey failed: %s", err)
}
testURL, err := url.Parse("https://example.com/")
if err != nil {
t.Fatalf("url.Parse failed: %s", err)
}
testURL.RawQuery = "∞"
marshalTests := []struct {
name string
template *Certificate
expectedError string
}{
{
name: "marshal: unicode dNSName",
template: &Certificate{
SerialNumber: big.NewInt(0),
DNSNames: []string{"∞"},
},
expectedError: "x509: \"∞\" cannot be encoded as an IA5String",
},
{
name: "marshal: unicode rfc822Name",
template: &Certificate{
SerialNumber: big.NewInt(0),
EmailAddresses: []string{"∞"},
},
expectedError: "x509: \"∞\" cannot be encoded as an IA5String",
},
{
name: "marshal: unicode uniformResourceIdentifier",
template: &Certificate{
SerialNumber: big.NewInt(0),
URIs: []*url.URL{testURL},
},
expectedError: "x509: \"https://example.com/?∞\" cannot be encoded as an IA5String",
},
}
for _, tc := range marshalTests {
t.Run(tc.name, func(t *testing.T) {
_, err := CreateCertificate(rand.Reader, tc.template, tc.template, k.Public(), k)
if err == nil {
t.Errorf("expected CreateCertificate to fail with template: %v", tc.template)
} else if err.Error() != tc.expectedError {
t.Errorf("unexpected error: got %q, want %q", err.Error(), tc.expectedError)
}
})
}
unmarshalTests := []struct {
name string
cert string
expectedError string
}{
{
name: "unmarshal: unicode dNSName",
cert: "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",
expectedError: "x509: SAN dNSName is malformed",
},
{
name: "unmarshal: unicode rfc822Name",
cert: "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",
expectedError: "x509: SAN rfc822Name is malformed",
},
{
name: "unmarshal: unicode uniformResourceIdentifier",
cert: "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",
expectedError: "x509: SAN uniformResourceIdentifier is malformed",
},
}
for _, tc := range unmarshalTests {
der, err := hex.DecodeString(tc.cert)
if err != nil {
t.Fatalf("failed to decode test cert: %s", err)
}
_, err = ParseCertificate(der)
if err == nil {
t.Error("expected CreateCertificate to fail")
} else if err.Error() != tc.expectedError {
t.Errorf("unexpected error: got %q, want %q", err.Error(), tc.expectedError)
}
}
}