Bugfixes in X509 decoder (#1927)

This PR fixes a few bugs:

- Support cases where the "version" field doesn't exist (the version in this case should be v1)
- Support cases where neither "extensions", "subject unique ID" and "issuer unique ID" exists
- Add tests for these cases

Author: seladb

Packet++/header/X509Decoder.h

@@ -596,10 +596,6 @@ namespace pcpp
 			int m_ExtensionsOffset = -1;
 
 			X509TBSCertificate(Asn1SequenceRecord* root);
-			int getIndex(int offset) const
-			{
-				return m_VersionOffset + offset;
-			}
 		};
 
 		/// @class X509Certificate

Packet++/src/X509Decoder.cpp

@@ -749,23 +749,26 @@ namespace pcpp
 				m_SubjectOffset = currIndex++;
 				m_SubjectPublicKeyInfoOffset = currIndex++;
 
-				record = root->getSubRecords().at(currIndex);
-
-				if (record->getTagClass() == Asn1TagClass::ContextSpecific && record->getTagType() == 1)
+				if (root->getSubRecords().size() > static_cast<size_t>(currIndex))
 				{
-					m_IssuerUniqueID = currIndex++;
 					record = root->getSubRecords().at(currIndex);
-				}
 
-				if (record->getTagClass() == Asn1TagClass::ContextSpecific && record->getTagType() == 2)
-				{
-					m_SubjectUniqueID = currIndex++;
-					record = root->getSubRecords().at(currIndex);
-				}
-
-				if (X509Extensions::isValidExtensionsRecord(record))
-				{
-					m_ExtensionsOffset = currIndex++;
+					if (record->getTagClass() == Asn1TagClass::ContextSpecific && record->getTagType() == 1)
+					{
+						m_IssuerUniqueID = currIndex++;
+						record = root->getSubRecords().at(currIndex);
+					}
+
+					if (record->getTagClass() == Asn1TagClass::ContextSpecific && record->getTagType() == 2)
+					{
+						m_SubjectUniqueID = currIndex++;
+						record = root->getSubRecords().at(currIndex);
+					}
+
+					if (X509Extensions::isValidExtensionsRecord(record))
+					{
+						m_ExtensionsOffset = currIndex++;
+					}
 				}
 			}
 			catch (const std::out_of_range&)
@@ -788,25 +791,25 @@ namespace pcpp
 
 		X509Name X509TBSCertificate::getIssuer() const
 		{
-			auto root = getSubRecordAndCast<Asn1SequenceRecord>(m_Root, getIndex(m_IssuerOffset), "Issuer");
+			auto root = getSubRecordAndCast<Asn1SequenceRecord>(m_Root, m_IssuerOffset, "Issuer");
 			return X509Name(root);
 		}
 
 		X509Validity X509TBSCertificate::getValidity() const
 		{
-			auto root = getSubRecordAndCast<Asn1SequenceRecord>(m_Root, getIndex(m_ValidityOffset), "Validity");
+			auto root = getSubRecordAndCast<Asn1SequenceRecord>(m_Root, m_ValidityOffset, "Validity");
 			return X509Validity(root);
 		}
 
 		X509Name X509TBSCertificate::getSubject() const
 		{
-			auto root = getSubRecordAndCast<Asn1SequenceRecord>(m_Root, getIndex(m_SubjectOffset), "Subject");
+			auto root = getSubRecordAndCast<Asn1SequenceRecord>(m_Root, m_SubjectOffset, "Subject");
 			return X509Name(root);
 		}
 
 		X509SubjectPublicKeyInfo X509TBSCertificate::getSubjectPublicKeyInfo() const
 		{
-			auto root = getSubRecordAndCast<Asn1SequenceRecord>(m_Root, getIndex(m_SubjectPublicKeyInfoOffset),
+			auto root = getSubRecordAndCast<Asn1SequenceRecord>(m_Root, m_SubjectPublicKeyInfoOffset,
 			                                                    "Subject Public Key Info");
 			return X509SubjectPublicKeyInfo(root);
 		}
@@ -818,7 +821,7 @@ namespace pcpp
 				return nullptr;
 			}
 
-			auto root = getSubRecordAndCast<Asn1ConstructedRecord>(m_Root, getIndex(m_ExtensionsOffset), "Extensions");
+			auto root = getSubRecordAndCast<Asn1ConstructedRecord>(m_Root, m_ExtensionsOffset, "Extensions");
 			return std::unique_ptr<X509Extensions>(new X509Extensions(root));
 		}
 
@@ -1015,9 +1018,13 @@ namespace pcpp
 	{
 		if (!m_ExtensionsParsed)
 		{
-			for (const auto& extension : m_TBSCertificate.getExtensions()->getExtensions())
+			auto extensions = m_TBSCertificate.getExtensions();
+			if (extensions != nullptr)
 			{
-				m_Extensions.emplace_back(X509Extension(extension));
+				for (const auto& extension : extensions->getExtensions())
+				{
+					m_Extensions.emplace_back(X509Extension(extension));
+				}
 			}
 			m_ExtensionsParsed = true;
 		}

Tests/Packet++Test/PacketExamples/x509_cert_no_version_extension_fields.pem

@@ -0,0 +1,21 @@
+-----BEGIN CERTIFICATE-----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+-----END CERTIFICATE-----

Tests/Packet++Test/Tests/X509Tests.cpp

@@ -329,6 +329,14 @@ PTF_TEST_CASE(X509VariantsParsingTest)
 		auto x509Cert = pcpp::X509Certificate::fromDERFile("PacketExamples/x509_cert_serial_lead_zeros.der");
 		PTF_ASSERT_EQUAL(x509Cert->getSerialNumber().toString(), "80");
 	}
+
+	// No version and extensions fields
+	{
+		auto x509Cert = pcpp::X509Certificate::fromPEMFile("PacketExamples/x509_cert_no_version_extension_fields.pem");
+		PTF_ASSERT_EQUAL(x509Cert->getVersion(), pcpp::X509Version::V1, enumclass);
+		PTF_ASSERT_EQUAL(x509Cert->getNotBefore().toString(), "2025-08-17 08:27:07");
+		PTF_ASSERT_EQUAL(x509Cert->getExtensions().size(), 0);
+	}
 }
 
 PTF_TEST_CASE(X509InvalidDataTest)