crypto/x509: handle CRLDistributionPoints without FullNames

Fixes #12910.

Change-Id: If446e5dce236483bbb898cc5959baf8371f05142
Reviewed-on: https://go-review.googlesource.com/17550Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Reviewed-by: Adam Langley <agl@golang.org>

src/crypto/x509/x509.go

@@ -1048,7 +1048,7 @@ func parseCertificate(in *certificate) (*Certificate, error) {
 				}
 
 			case 31:
-				// RFC 5280, 4.2.1.14
+				// RFC 5280, 4.2.1.13
 
 				// CRLDistributionPoints ::= SEQUENCE SIZE (1..MAX) OF DistributionPoint
 				//
@@ -1069,6 +1069,11 @@ func parseCertificate(in *certificate) (*Certificate, error) {
 				}
 
 				for _, dp := range cdp {
+					// Per RFC 5280, 4.2.1.13, one of distributionPoint or cRLIssuer may be empty.
+					if len(dp.DistributionPoint.FullName.Bytes) == 0 {
+						continue
+					}
+
 					var n asn1.RawValue
 					if _, err := asn1.Unmarshal(dp.DistributionPoint.FullName.Bytes, &n); err != nil {
 						return nil, err