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Add lint to cover TLS BR v2 EKU checks #833
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christopher-henderson
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vanbroup:e_sub_cert_eku_check
Apr 28, 2024
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5f32586
Add EV policy and Pre Certiicate Signing Certificate EKU
vanbroup 816b156
Apply serverAuth to certificates with CA/B TLS policy OID
vanbroup a1f6f24
lint subscriber EKU according to TLS BR v2
vanbroup 237965d
Make lint ineffective since TLS BR v2
vanbroup e83c664
Correct expected result
vanbroup 15db930
Correct numbers as result of CA/B policy inclusion in additon to serv…
vanbroup 4e27fe5
Check if subscriber certificate with EKU extension
vanbroup 8d4f254
Pass certificate in subscriber certificate check
vanbroup 7d05f9f
Remove unnecessary len check
vanbroup 8bcd48c
Format
vanbroup 20a483c
Merge branch 'master' into e_sub_cert_eku_check
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,81 @@ | ||
| package cabf_br | ||
|
|
||
| /* | ||
| * ZLint Copyright 2024 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. | ||
| */ | ||
|
|
||
| import ( | ||
| "fmt" | ||
|
|
||
| "github.com/zmap/zcrypto/x509" | ||
| "github.com/zmap/zlint/v3/lint" | ||
| "github.com/zmap/zlint/v3/util" | ||
| ) | ||
|
|
||
| type subExtKeyUsageCheck struct{} | ||
|
|
||
| func init() { | ||
| lint.RegisterCertificateLint(&lint.CertificateLint{ | ||
| LintMetadata: lint.LintMetadata{ | ||
| Name: "e_sub_cert_eku_check", | ||
| Description: "Subscriber certificates MUST have id-kp-serverAuth and MAY have id-kp-clientAuth present in extKeyUsage", | ||
| Citation: "BRs: 7.1.2.7.10 Subscriber Certificate Extended Key Usage", | ||
| Source: lint.CABFBaselineRequirements, | ||
| EffectiveDate: util.CABFBRs_2_0_0_Date, | ||
| }, | ||
| Lint: NewSubExtKeyUsageCheck, | ||
| }) | ||
| } | ||
|
|
||
| func NewSubExtKeyUsageCheck() lint.LintInterface { | ||
| return &subExtKeyUsageCheck{} | ||
| } | ||
|
|
||
| func (l *subExtKeyUsageCheck) CheckApplies(c *x509.Certificate) bool { | ||
| return util.IsSubscriberCert(c) && util.IsExtInCert(c, util.EkuSynOid) | ||
| } | ||
|
|
||
| func (l *subExtKeyUsageCheck) Execute(c *x509.Certificate) *lint.LintResult { | ||
| var hasClientAuthEKU, hasServerAuthEKU bool | ||
|
|
||
| for _, eku := range c.ExtKeyUsage { | ||
| switch eku { | ||
| case x509.ExtKeyUsageServerAuth: | ||
| hasServerAuthEKU = true | ||
|
|
||
| case x509.ExtKeyUsageClientAuth: | ||
| hasClientAuthEKU = true | ||
|
|
||
| case x509.ExtKeyUsageAny, x509.ExtKeyUsageCodeSigning, x509.ExtKeyUsageTimeStamping, | ||
| x509.ExtKeyUsageOcspSigning, x509.ExtKeyUsageEmailProtection: | ||
|
|
||
| return &lint.LintResult{Status: lint.Error, Details: fmt.Sprintf("%s MUST NOT be present", util.GetEKUString(eku))} | ||
| } | ||
| } | ||
|
|
||
| if !hasServerAuthEKU { | ||
| return &lint.LintResult{Status: lint.Error, Details: "id-kp-serverAuth MUST be present"} | ||
| } | ||
|
|
||
| for _, eku := range c.UnknownExtKeyUsage { | ||
| if eku.Equal(util.PreCertificateSigningCertificateEKU) { | ||
| return &lint.LintResult{Status: lint.Error, Details: "Precertificate Signing Certificate extKeyUsage MUST NOT be present"} | ||
| } | ||
| } | ||
|
|
||
| if (len(c.ExtKeyUsage) > 2 && !hasClientAuthEKU) || len(c.UnknownExtKeyUsage) > 0 { | ||
| return &lint.LintResult{Status: lint.Warn, Details: "any other value than id-kp-serverAuth and id-kp-clientAuth is NOT RECOMMENDED"} | ||
| } | ||
|
|
||
| return &lint.LintResult{Status: lint.Pass} | ||
| } | ||
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,75 @@ | ||
| package cabf_br | ||
|
|
||
| /* | ||
| * ZLint Copyright 2024 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. | ||
| */ | ||
|
|
||
| import ( | ||
| "testing" | ||
|
|
||
| "github.com/zmap/zlint/v3/lint" | ||
| "github.com/zmap/zlint/v3/test" | ||
| ) | ||
|
|
||
| func TestSubExtKeyUsageCheck(t *testing.T) { | ||
| testCases := []struct { | ||
| Name string | ||
| InputFilename string | ||
| ExpectedResult lint.LintStatus | ||
| }{ | ||
| { | ||
| Name: "pass - serverAuth EKU", | ||
| InputFilename: "subExtKeyUsageServerAuth.pem", | ||
| ExpectedResult: lint.Pass, | ||
| }, | ||
| { | ||
| Name: "pass - serverAuth and clientAuth EKU", | ||
| InputFilename: "subExtKeyUSageServerAndClientAuth.pem", | ||
| ExpectedResult: lint.Pass, | ||
| }, | ||
| { | ||
| Name: "error - only clientAuth EKU with CA/B TLS BR policy OID", | ||
| InputFilename: "subExtKeyUsageClientAuth.pem", | ||
| ExpectedResult: lint.Error, | ||
| }, | ||
| { | ||
| Name: "ne - only clientAuth EKU, with CA/B TLS BR policy OID, NotBefore before effective date", | ||
| InputFilename: "subExtKeyUsageClientAuthPreBRv2.pem", | ||
| ExpectedResult: lint.NE, | ||
| }, | ||
| { | ||
| Name: "error - serverAuth and timeStamping EKU", | ||
| InputFilename: "subExtKeyUsageServerAuthAndTimeStamping.pem", | ||
| ExpectedResult: lint.Error, | ||
| }, | ||
| { | ||
| Name: "error - serverAuth and unknown PreCertSigCert EKU", | ||
| InputFilename: "subExtKeyUsageServerAuthAndPreCertSigCert.pem", | ||
| ExpectedResult: lint.Error, | ||
| }, | ||
| { | ||
| Name: "warn - serverAuth and MicrosoftDocumentSigning EKU", | ||
| InputFilename: "subExtKeyUsageServerAuthAndUnknown.pem", | ||
| ExpectedResult: lint.Warn, | ||
| }, | ||
| } | ||
|
|
||
| for _, tc := range testCases { | ||
| t.Run(tc.Name, func(t *testing.T) { | ||
| result := test.TestLint("e_sub_cert_eku_check", tc.InputFilename) | ||
| if result.Status != tc.ExpectedResult { | ||
| t.Errorf("expected result %v was %v - details: %v", tc.ExpectedResult, result.Status, result.Details) | ||
| } | ||
| }) | ||
| } | ||
| } |
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,38 @@ | ||
| Certificate: | ||
| Data: | ||
| Version: 3 (0x2) | ||
| Serial Number: 3 (0x3) | ||
| Signature Algorithm: ecdsa-with-SHA256 | ||
| Issuer: | ||
| Validity | ||
| Not Before: Sep 15 12:00:00 2023 GMT | ||
| Not After : Sep 15 12:00:00 2024 GMT | ||
| Subject: | ||
| Subject Public Key Info: | ||
| Public Key Algorithm: id-ecPublicKey | ||
| Public-Key: (256 bit) | ||
| pub: | ||
| 04:f1:d5:c1:b1:f9:0f:63:d7:c2:ba:83:a3:c6:b7: | ||
| fb:cf:07:bb:c7:33:03:61:4d:13:0f:45:46:8d:47: | ||
| 7f:41:ce:8f:9f:1f:85:37:ee:ff:30:00:37:3c:53: | ||
| 8b:60:aa:38:48:a8:5c:ca:c7:0c:78:12:f4:2e:ca: | ||
| 62:d8:f7:6c:b5 | ||
| ASN1 OID: prime256v1 | ||
| NIST CURVE: P-256 | ||
| X509v3 extensions: | ||
| X509v3 Extended Key Usage: | ||
| TLS Web Server Authentication, TLS Web Client Authentication | ||
| Signature Algorithm: ecdsa-with-SHA256 | ||
| Signature Value: | ||
| 30:45:02:20:79:05:6d:37:0a:db:85:a5:6f:54:68:1d:37:50: | ||
| 33:ce:4a:97:d6:59:77:d3:98:1b:df:89:43:f9:02:d8:e2:91: | ||
| 02:21:00:83:cd:55:a0:54:f1:88:be:71:23:96:7b:4c:38:6a: | ||
| d6:14:2c:dc:e0:75:e8:51:c3:bd:bc:09:74:63:5e:3d:7b | ||
| -----BEGIN CERTIFICATE----- | ||
| MIIBDzCBtqADAgECAgEDMAoGCCqGSM49BAMCMAAwHhcNMjMwOTE1MTIwMDAwWhcN | ||
| MjQwOTE1MTIwMDAwWjAAMFkwEwYHKoZIzj0CAQYIKoZIzj0DAQcDQgAE8dXBsfkP | ||
| Y9fCuoOjxrf7zwe7xzMDYU0TD0VGjUd/Qc6Pnx+FN+7/MAA3PFOLYKo4SKhcyscM | ||
| eBL0Lspi2PdstaMhMB8wHQYDVR0lBBYwFAYIKwYBBQUHAwEGCCsGAQUFBwMCMAoG | ||
| CCqGSM49BAMCA0gAMEUCIHkFbTcK24Wlb1RoHTdQM85Kl9ZZd9OYG9+JQ/kC2OKR | ||
| AiEAg81VoFTxiL5xI5Z7TDhq1hQs3OB16FHDvbwJdGNePXs= | ||
| -----END CERTIFICATE----- |
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,40 @@ | ||
| Certificate: | ||
| Data: | ||
| Version: 3 (0x2) | ||
| Serial Number: 3 (0x3) | ||
| Signature Algorithm: ecdsa-with-SHA256 | ||
| Issuer: | ||
| Validity | ||
| Not Before: Sep 15 12:00:00 2023 GMT | ||
| Not After : Sep 15 12:00:00 2024 GMT | ||
| Subject: | ||
| Subject Public Key Info: | ||
| Public Key Algorithm: id-ecPublicKey | ||
| Public-Key: (256 bit) | ||
| pub: | ||
| 04:04:3b:ca:38:58:01:84:3c:49:f1:45:a8:b6:02: | ||
| 18:00:dc:f3:3d:78:2b:d0:ff:3d:16:62:07:4d:2e: | ||
| 63:e0:92:0b:45:fc:f8:90:90:ce:bf:b6:db:ba:60: | ||
| e5:d2:fb:b0:f7:d1:39:18:7a:40:a9:7d:e3:22:ac: | ||
| ef:e9:f6:70:4c | ||
| ASN1 OID: prime256v1 | ||
| NIST CURVE: P-256 | ||
| X509v3 extensions: | ||
| X509v3 Extended Key Usage: | ||
| TLS Web Client Authentication | ||
| X509v3 Certificate Policies: | ||
| Policy: 2.23.140.1.2.1 | ||
| Signature Algorithm: ecdsa-with-SHA256 | ||
| Signature Value: | ||
| 30:44:02:20:25:79:7b:74:45:0d:29:f9:24:f0:81:4d:03:e4: | ||
| e0:b6:01:19:31:ee:dc:81:e6:bb:2a:88:91:ae:cd:d5:8e:5a: | ||
| 02:20:03:2f:9a:da:62:e6:d4:8f:96:99:f4:ea:22:0d:23:e0: | ||
| a4:9b:eb:42:08:9f:47:ff:50:ba:e7:f1:e7:9f:15:39 | ||
| -----BEGIN CERTIFICATE----- | ||
| MIIBGTCBwaADAgECAgEDMAoGCCqGSM49BAMCMAAwHhcNMjMwOTE1MTIwMDAwWhcN | ||
| MjQwOTE1MTIwMDAwWjAAMFkwEwYHKoZIzj0CAQYIKoZIzj0DAQcDQgAEBDvKOFgB | ||
| hDxJ8UWotgIYANzzPXgr0P89FmIHTS5j4JILRfz4kJDOv7bbumDl0vuw99E5GHpA | ||
| qX3jIqzv6fZwTKMsMCowEwYDVR0lBAwwCgYIKwYBBQUHAwIwEwYDVR0gBAwwCjAI | ||
| BgZngQwBAgEwCgYIKoZIzj0EAwIDRwAwRAIgJXl7dEUNKfkk8IFNA+TgtgEZMe7c | ||
| gea7KoiRrs3VjloCIAMvmtpi5tSPlpn06iINI+Ckm+tCCJ9H/1C65/HnnxU5 | ||
| -----END CERTIFICATE----- |
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Maybe you could set a variable in the
defaultcase in therange c.ExtKeyUsageloop and check that.There was a problem hiding this comment.
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I may advocate for keeping a list of of OIDs found during the execution of the lint and cross referencing them at them end against the list of known OIDs.
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The ExtKeyUsage and UnknownExtKeyUsage are not of the same type:
The lint currently checks for MUST, MUST NOT, MAY, and NOT RECOMMENDED, and returns the corresponding lint status and error.
We can create a map with each EKU and the requirement (i.e., MUST) and lookup the value while ranging over the two EKU lists, but I guess this would be less efficient
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I reckon that this would be an efficiency modifier in the range of nanoseconds (possibly into ms) for each run of the lint. In general, legibility trumps such optimizations since correctness of the lint is paramount.