Lint for CABF SMIME 7.1.2.3.h - subjectAlternativeName SHOULD NOT be …

…marked critical unless the subject field is an empty sequence (#746) * Lint for CABF SMIME 7.1.2.3.h - subjectAlternativeName SHOULD NOT be marked critical unless the subject field is an empty sequence. * removing implied warning interpretation
zmap · Oct 15, 2023 · 88e01ad · 88e01ad
1 parent 08a9354
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diff --git a/v3/lints/cabf_smime_br/lint_san_should_not_be_critical.go b/v3/lints/cabf_smime_br/lint_san_should_not_be_critical.go
@@ -0,0 +1,64 @@
+/*
+ * ZLint Copyright 2023 Regents of the University of Michigan
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License"); you may not
+ * use this file except in compliance with the License. You may obtain a copy
+ * of the License at http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or
+ * implied. See the License for the specific language governing
+ * permissions and limitations under the License.
+ */
+
+package cabf_smime_br
+
+import (
+	"reflect"
+
+	"github.com/zmap/zcrypto/x509"
+	"github.com/zmap/zcrypto/x509/pkix"
+	"github.com/zmap/zlint/v3/lint"
+	"github.com/zmap/zlint/v3/util"
+)
+
+func init() {
+	lint.RegisterLint(&lint.Lint{
+		Name:          "w_san_should_not_be_critical",
+		Description:   "subjectAlternativeName SHOULD NOT be marked critical unless the subject field is an empty sequence.",
+		Citation:      "7.1.2.3.h",
+		Source:        lint.CABFSMIMEBaselineRequirements,
+		EffectiveDate: util.CABF_SMIME_BRs_1_0_0_Date,
+		Lint:          NewSubjectAlternativeNameNotCritical,
+	})
+}
+
+type SubjectAlternativeNameNotCritical struct{}
+
+func NewSubjectAlternativeNameNotCritical() lint.LintInterface {
+	return &SubjectAlternativeNameNotCritical{}
+}
+
+func (l *SubjectAlternativeNameNotCritical) CheckApplies(c *x509.Certificate) bool {
+	return util.IsSubscriberCert(c) && util.IsExtInCert(c, util.SubjectAlternateNameOID)
+}
+
+func (l *SubjectAlternativeNameNotCritical) Execute(c *x509.Certificate) *lint.LintResult {
+	san := util.GetExtFromCert(c, util.SubjectAlternateNameOID)
+	isCritical := san.Critical
+	emptySubject := reflect.DeepEqual(c.Subject, pkix.Name{OriginalRDNS: pkix.RDNSequence{}})
+	if isCritical && emptySubject {
+		// "...unless the subject field is an empty sequence"
+		return &lint.LintResult{Status: lint.Pass}
+	} else if isCritical && !emptySubject {
+		// Critical, but there's a non-empty SAN.
+		return &lint.LintResult{
+			Status:  lint.Warn,
+			Details: "subject is not empty, but subjectAlternativeName is marked critical",
+		}
+	} else {
+		// Not critical, not empty SAN.
+		return &lint.LintResult{Status: lint.Pass}
+	}
+}
diff --git a/v3/lints/cabf_smime_br/lint_san_should_not_be_critical_test.go b/v3/lints/cabf_smime_br/lint_san_should_not_be_critical_test.go
@@ -0,0 +1,34 @@
+package cabf_smime_br
+
+import (
+	"testing"
+
+	"github.com/zmap/zlint/v3/lint"
+	"github.com/zmap/zlint/v3/test"
+)
+
+func TestSubjectAlternativeNameNotCritical(t *testing.T) {
+	testCases := []struct {
+		Name           string
+		InputFilename  string
+		ExpectedResult lint.LintStatus
+	}{
+		{
+			Name:           "pass - cert without a CRL distribution point",
+			InputFilename:  "smime/san_not_critical_with_subject.pem",
+			ExpectedResult: lint.Pass,
+		},
+		// I admit that it is very difficult to construct a negative case
+		// since the Go standard library does the correct thing on your
+		// behalf at time of signing. Plus no certs came up bad in
+		// the test corpus, so we don't have any live examples.
+	}
+	for _, tc := range testCases {
+		t.Run(tc.Name, func(t *testing.T) {
+			result := test.TestLint("w_san_should_not_be_critical", tc.InputFilename)
+			if result.Status != tc.ExpectedResult {
+				t.Errorf("expected result %v was %v - details: %v", tc.ExpectedResult, result.Status, result.Details)
+			}
+		})
+	}
+}
diff --git a/v3/testdata/smime/san_not_critical_with_empty_subject.pem b/v3/testdata/smime/san_not_critical_with_empty_subject.pem
@@ -0,0 +1,41 @@
+Certificate:
+    Data:
+        Version: 3 (0x2)
+        Serial Number: 3 (0x3)
+        Signature Algorithm: ecdsa-with-SHA256
+        Issuer: 
+        Validity
+            Not Before: Sep 30 16:12:15 2023 GMT
+            Not After : Nov 30 00:00:00 9998 GMT
+        Subject: 
+        Subject Public Key Info:
+            Public Key Algorithm: id-ecPublicKey
+                Public-Key: (256 bit)
+                pub:
+                    04:83:07:4d:66:ba:e8:dd:7c:ed:7a:02:67:9d:80:
+                    7d:a5:2c:a4:bc:6f:df:aa:9c:3a:f7:6b:50:ae:42:
+                    36:5c:71:54:88:8e:79:f3:e3:d2:d0:72:26:c1:19:
+                    9d:28:a9:4f:71:c9:65:ea:40:40:4f:f6:86:d5:fb:
+                    77:d9:68:dc:21
+                ASN1 OID: prime256v1
+                NIST CURVE: P-256
+        X509v3 extensions:
+            X509v3 Extended Key Usage: 
+                E-mail Protection
+            X509v3 Subject Alternative Name: 
+                email:coolguy@coolplace.come
+    Signature Algorithm: ecdsa-with-SHA256
+    Signature Value:
+        30:46:02:21:00:c0:a2:c4:c3:f3:b4:27:39:b5:8b:85:c4:5a:
+        60:67:27:d1:7c:b4:db:3b:7e:0d:9f:2c:81:0a:5f:f6:8a:e0:
+        0a:02:21:00:ec:06:77:d2:09:41:74:e8:8c:9b:64:72:27:fc:
+        e0:ab:62:fa:2b:bf:94:30:49:24:92:56:d9:e6:65:ba:86:6d
+-----BEGIN CERTIFICATE-----
+MIIBKzCB0aADAgECAgEDMAoGCCqGSM49BAMCMAAwIBcNMjMwOTMwMTYxMjE1WhgP
+OTk5ODExMzAwMDAwMDBaMAAwWTATBgcqhkjOPQIBBggqhkjOPQMBBwNCAASDB01m
+uujdfO16AmedgH2lLKS8b9+qnDr3a1CuQjZccVSIjnnz49LQcibBGZ0oqU9xyWXq
+QEBP9obV+3fZaNwhozowODATBgNVHSUEDDAKBggrBgEFBQcDBDAhBgNVHREEGjAY
+gRZjb29sZ3V5QGNvb2xwbGFjZS5jb21lMAoGCCqGSM49BAMCA0kAMEYCIQDAosTD
+87QnObWLhcRaYGcn0Xy02zt+DZ8sgQpf9orgCgIhAOwGd9IJQXTojJtkcif84Kti
++iu/lDBJJJJW2eZluoZt
+-----END CERTIFICATE-----
diff --git a/v3/testdata/smime/san_not_critical_with_subject.pem b/v3/testdata/smime/san_not_critical_with_subject.pem
@@ -0,0 +1,41 @@
+Certificate:
+    Data:
+        Version: 3 (0x2)
+        Serial Number: 3 (0x3)
+        Signature Algorithm: ecdsa-with-SHA256
+        Issuer: 
+        Validity
+            Not Before: Sep 30 16:52:30 2023 GMT
+            Not After : Nov 30 00:00:00 9998 GMT
+        Subject: CN = Bartholomew Kuma
+        Subject Public Key Info:
+            Public Key Algorithm: id-ecPublicKey
+                Public-Key: (256 bit)
+                pub:
+                    04:a2:02:fe:ab:17:45:2b:67:21:b9:57:42:17:1d:
+                    bf:e7:11:aa:b0:a7:71:7b:87:b9:4b:79:54:09:9e:
+                    e1:7b:3b:6b:ed:fb:3c:0f:86:4d:94:b3:69:1b:30:
+                    98:15:69:8d:09:06:09:84:62:6c:02:c7:01:f5:75:
+                    cb:c8:78:31:df
+                ASN1 OID: prime256v1
+                NIST CURVE: P-256
+        X509v3 extensions:
+            X509v3 Extended Key Usage: 
+                E-mail Protection
+            X509v3 Subject Alternative Name: 
+                email:coolguy@coolplace.come
+    Signature Algorithm: ecdsa-with-SHA256
+    Signature Value:
+        30:45:02:21:00:bd:fb:e1:0b:c1:26:2a:85:bf:95:6a:dc:37:
+        9a:b9:67:95:ba:43:6d:d1:8d:4d:aa:53:54:70:72:30:f0:24:
+        ca:02:20:2e:61:95:23:b8:39:a7:48:02:59:d9:a3:9b:36:c6:
+        c8:95:06:4e:36:63:85:a0:19:88:23:ad:a9:d4:37:6d:44
+-----BEGIN CERTIFICATE-----
+MIIBRTCB7KADAgECAgEDMAoGCCqGSM49BAMCMAAwIBcNMjMwOTMwMTY1MjMwWhgP
+OTk5ODExMzAwMDAwMDBaMBsxGTAXBgNVBAMTEEJhcnRob2xvbWV3IEt1bWEwWTAT
+BgcqhkjOPQIBBggqhkjOPQMBBwNCAASiAv6rF0UrZyG5V0IXHb/nEaqwp3F7h7lL
+eVQJnuF7O2vt+zwPhk2Us2kbMJgVaY0JBgmEYmwCxwH1dcvIeDHfozowODATBgNV
+HSUEDDAKBggrBgEFBQcDBDAhBgNVHREEGjAYgRZjb29sZ3V5QGNvb2xwbGFjZS5j
+b21lMAoGCCqGSM49BAMCA0gAMEUCIQC9++ELwSYqhb+Vatw3mrlnlbpDbdGNTapT
+VHByMPAkygIgLmGVI7g5p0gCWdmjmzbGyJUGTjZjhaAZiCOtqdQ3bUQ=
+-----END CERTIFICATE-----