Add missing validity checks to CSR verification (#22069)

* Add missing validity checks to CSR verification

- SDK's CSR verification (VerifyCertificateSigningRequest) allowed trailing
  garbage past the end of the buffer if the primary SEQUENCE element is OK
  and checks-out. This is looser enforcement than some crypto libraries
  which expect a CSR to be 100% valid ASN.1 DER and have no unnecessary bytes
  or otherwise unparsable bytes.

Fixes #22068

This PR:
- Adds validity checks for size and basic format that catches
  the problem.
- Adds unit tests that use externally generated CSRs to validate
  the `VerifyCertificateSigningRequest` logic, rather than only
  relying on round-trips with generation.

Testing done:
- Added new unit tests. Existing unit tests pass
- Tested under OpenSSL, BoringSSL and mbedTLS

* Fix docs typo

src/crypto/CHIPCryptoPAL.cpp

@@ -1092,5 +1092,28 @@ CHIP_ERROR GenerateCertificateSigningRequest(const P256Keypair * keypair, Mutabl
     return err;
 }
 
+CHIP_ERROR VerifyCertificateSigningRequestFormat(const uint8_t * csr, size_t csr_length)
+{
+    // Ensure we have enough size to validate header
+    VerifyOrReturnError((csr_length >= 16) && (csr_length <= kMAX_CSR_Length), CHIP_ERROR_UNSUPPORTED_CERT_FORMAT);
+
+    Reader reader(csr, csr_length);
+
+    // Ensure we have an outermost SEQUENCE
+    uint8_t seq_header = 0;
+    ReturnErrorOnFailure(reader.Read8(&seq_header).StatusCode());
+    VerifyOrReturnError(seq_header == kSeqTag, CHIP_ERROR_UNSUPPORTED_CERT_FORMAT);
+
+    uint8_t seq_length = 0;
+    VerifyOrReturnError(ReadDerLength(reader, seq_length) == CHIP_NO_ERROR, CHIP_ERROR_UNSUPPORTED_CERT_FORMAT);
+
+    // Ensure that outer length matches sequence length + tag overhead, otherwise
+    // we have trailing garbage
+    size_t header_overhead = (seq_length <= 127) ? 2 : 3;
+    VerifyOrReturnError(csr_length == (seq_length + header_overhead), CHIP_ERROR_UNSUPPORTED_CERT_FORMAT);
+
+    return CHIP_NO_ERROR;
+}
+
 } // namespace Crypto
 } // namespace chip

src/crypto/CHIPCryptoPAL.h

@@ -640,8 +640,23 @@ CHIP_ERROR AES_CCM_decrypt(const uint8_t * ciphertext, size_t ciphertext_length,
  **/
 CHIP_ERROR GenerateCertificateSigningRequest(const P256Keypair * keypair, MutableByteSpan & csr_span);
 
+/**
+ * @brief Common code to validate ASN.1 format/size of a CSR, used by VerifyCertificateSigningRequest.
+ *
+ * Ensures it's not obviously malformed and doesn't have trailing garbage.
+ *
+ * @param csr CSR in DER format
+ * @param csr_length The length of the CSR buffer
+ * @return CHIP_ERROR_UNSUPPORTED_CERT_FORMAT on invalid format, CHIP_NO_ERROR otherwise.
+ */
+CHIP_ERROR VerifyCertificateSigningRequestFormat(const uint8_t * csr, size_t csr_length);
+
 /**
  * @brief Verify the Certificate Signing Request (CSR). If successfully verified, it outputs the public key from the CSR.
+ *
+ * The CSR is valid if the format is correct, the signature validates with the embedded public
+ * key, and there is no trailing garbage data.
+ *
  * @param csr CSR in DER format
  * @param csr_length The length of the CSR
  * @param pubkey The public key from the verified CSR

src/crypto/CHIPCryptoPALOpenSSL.cpp

@@ -1254,6 +1254,8 @@ CHIP_ERROR P256Keypair::NewCertificateSigningRequest(uint8_t * out_csr, size_t &
 
 CHIP_ERROR VerifyCertificateSigningRequest(const uint8_t * csr, size_t csr_length, P256PublicKey & pubkey)
 {
+    ReturnErrorOnFailure(VerifyCertificateSigningRequestFormat(csr, csr_length));
+
     ERR_clear_error();
     CHIP_ERROR error = CHIP_NO_ERROR;
     int result       = 0;

src/crypto/CHIPCryptoPALTinyCrypt.cpp

@@ -777,6 +777,8 @@ CHIP_ERROR P256Keypair::NewCertificateSigningRequest(uint8_t * out_csr, size_t &
 CHIP_ERROR VerifyCertificateSigningRequest(const uint8_t * csr_buf, size_t csr_length, P256PublicKey & pubkey)
 {
 #if defined(MBEDTLS_X509_CSR_PARSE_C)
+    ReturnErrorOnFailure(VerifyCertificateSigningRequestFormat(csr_buf, csr_length));
+
     // TODO: For some embedded targets, mbedTLS library doesn't have mbedtls_x509_csr_parse_der, and mbedtls_x509_csr_parse_free.
     //       Taking a step back, embedded targets likely will not process CSR requests. Adding this action item to reevaluate
     //       this if there's a need for this processing for embedded targets.

src/crypto/CHIPCryptoPALmbedTLS.cpp

@@ -889,6 +889,8 @@ CHIP_ERROR P256Keypair::NewCertificateSigningRequest(uint8_t * out_csr, size_t &
 CHIP_ERROR VerifyCertificateSigningRequest(const uint8_t * csr_buf, size_t csr_length, P256PublicKey & pubkey)
 {
 #if defined(MBEDTLS_X509_CSR_PARSE_C)
+    ReturnErrorOnFailure(VerifyCertificateSigningRequestFormat(csr_buf, csr_length));
+
     // TODO: For some embedded targets, mbedTLS library doesn't have mbedtls_x509_csr_parse_der, and mbedtls_x509_csr_parse_free.
     //       Taking a step back, embedded targets likely will not process CSR requests. Adding this action item to reevaluate
     //       this if there's a need for this processing for embedded targets.

src/crypto/tests/CHIPCryptoPALTest.cpp

@@ -1034,6 +1034,170 @@ static void TestP256_Keygen(nlTestSuite * inSuite, void * inContext)
     NL_TEST_ASSERT(inSuite, keypair.Pubkey().ECDSA_validate_msg_signature(test_msg, msglen, test_sig) == CHIP_NO_ERROR);
 }
 
+void TestCSR_Verify(nlTestSuite * inSuite, void * inContext)
+{
+    Crypto::P256PublicKey pubKey;
+    CHIP_ERROR err;
+
+    // First case: there is trailing garbage in the CSR
+    {
+        const uint8_t kBadTrailingGarbageCsr[255] = {
+            0x30, 0x81, 0xda, 0x30, 0x81, 0x81, 0x02, 0x01, 0x00, 0x30, 0x0e, 0x31, 0x0c, 0x30, 0x0a, 0x06, 0x03, 0x55, 0x04, 0x0b,
+            0x0c, 0x03, 0x43, 0x53, 0x41, 0x30, 0x59, 0x30, 0x13, 0x06, 0x07, 0x2a, 0x86, 0x48, 0xce, 0x3d, 0x02, 0x01, 0x06, 0x08,
+            0x2a, 0x86, 0x48, 0xce, 0x3d, 0x03, 0x01, 0x07, 0x03, 0x42, 0x00, 0x04, 0x72, 0x48, 0xc0, 0x36, 0xf0, 0x12, 0x5f, 0xd1,
+            0x68, 0x92, 0x2d, 0xee, 0x57, 0x2b, 0x8e, 0x20, 0x9d, 0x97, 0xfa, 0x73, 0x92, 0xf1, 0xa0, 0x91, 0x0e, 0xfd, 0x04, 0x93,
+            0x66, 0x47, 0x3c, 0xa3, 0xf0, 0xa8, 0x47, 0xa1, 0xa3, 0x1e, 0x13, 0x3b, 0x67, 0x3b, 0x18, 0xca, 0x77, 0xd1, 0xea, 0xe3,
+            0x74, 0x93, 0x49, 0x8b, 0x9d, 0xdc, 0xef, 0xf9, 0xd5, 0x9b, 0x27, 0x19, 0xad, 0x6e, 0x90, 0xd2, 0xa0, 0x11, 0x30, 0x0f,
+            0x06, 0x09, 0x2a, 0x86, 0x48, 0x86, 0xf7, 0x0d, 0x01, 0x09, 0x0e, 0x31, 0x02, 0x30, 0x00, 0x30, 0x0a, 0x06, 0x08, 0x2a,
+            0x86, 0x48, 0xce, 0x3d, 0x04, 0x03, 0x02, 0x03, 0x48, 0x00, 0x30, 0x45, 0x02, 0x20, 0x6a, 0x2e, 0x15, 0x34, 0x1b, 0xde,
+            0xcb, 0x8f, 0xd2, 0xfd, 0x35, 0x03, 0x89, 0x0e, 0xed, 0x23, 0x54, 0xff, 0xcb, 0x79, 0xf9, 0xcb, 0x40, 0x33, 0x59, 0xb4,
+            0x27, 0x69, 0xeb, 0x07, 0x3b, 0xd5, 0x02, 0x21, 0x00, 0xb0, 0x25, 0xc9, 0xc2, 0x21, 0xe8, 0x54, 0xcc, 0x08, 0x12, 0xf5,
+            0x10, 0x3a, 0x0b, 0x25, 0x20, 0x0a, 0x61, 0x38, 0xc8, 0x6f, 0x82, 0xa7, 0x51, 0x84, 0x61, 0xae, 0x93, 0x69, 0xe4, 0x74,
+            0x84, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
+            0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
+        };
+
+        Crypto::ClearSecretData(pubKey.Bytes(), pubKey.Length());
+
+        err = VerifyCertificateSigningRequest(&kBadTrailingGarbageCsr[0], sizeof(kBadTrailingGarbageCsr), pubKey);
+
+        // On first test case, check if CSRs are supported at all, and skip test if they are not.
+        if (err == CHIP_ERROR_UNSUPPORTED_CHIP_FEATURE)
+        {
+            ChipLogError(Crypto, "The current platform does not support CSR parsing.");
+            return;
+        }
+
+        NL_TEST_ASSERT(inSuite, err != CHIP_NO_ERROR);
+
+        err = VerifyCertificateSigningRequestFormat(&kBadTrailingGarbageCsr[0], sizeof(kBadTrailingGarbageCsr));
+        NL_TEST_ASSERT(inSuite, err == CHIP_ERROR_UNSUPPORTED_CERT_FORMAT);
+    }
+
+    // Second case: correct CSR
+    {
+        const uint8_t kGoodCsr[205] = {
+            0x30, 0x81, 0xca, 0x30, 0x70, 0x02, 0x01, 0x00, 0x30, 0x0e, 0x31, 0x0c, 0x30, 0x0a, 0x06, 0x03, 0x55, 0x04, 0x0a,
+            0x0c, 0x03, 0x43, 0x53, 0x52, 0x30, 0x59, 0x30, 0x13, 0x06, 0x07, 0x2a, 0x86, 0x48, 0xce, 0x3d, 0x02, 0x01, 0x06,
+            0x08, 0x2a, 0x86, 0x48, 0xce, 0x3d, 0x03, 0x01, 0x07, 0x03, 0x42, 0x00, 0x04, 0xa3, 0xbe, 0xa1, 0xf5, 0x42, 0x01,
+            0x07, 0x3c, 0x4b, 0x75, 0x85, 0xd8, 0xe2, 0x98, 0xac, 0x2f, 0xf6, 0x98, 0xdb, 0xd9, 0x5b, 0xe0, 0x7e, 0xc1, 0x04,
+            0xd5, 0x73, 0xc5, 0xb0, 0x90, 0x77, 0x27, 0x00, 0x1e, 0x22, 0xc7, 0x89, 0x5e, 0x4d, 0x75, 0x07, 0x89, 0x82, 0x0f,
+            0x49, 0xb6, 0x59, 0xd5, 0xc5, 0x15, 0x7d, 0x93, 0xe6, 0x80, 0x5c, 0x70, 0x89, 0x0a, 0x43, 0x10, 0x3d, 0xeb, 0x3d,
+            0x4a, 0xa0, 0x00, 0x30, 0x0c, 0x06, 0x08, 0x2a, 0x86, 0x48, 0xce, 0x3d, 0x04, 0x03, 0x02, 0x05, 0x00, 0x03, 0x48,
+            0x00, 0x30, 0x45, 0x02, 0x20, 0x1d, 0x86, 0x21, 0xb4, 0xc2, 0xe1, 0xa9, 0xf3, 0xbc, 0xc8, 0x7c, 0xda, 0xb4, 0xb9,
+            0xc6, 0x8c, 0xd0, 0xe4, 0x9a, 0x9c, 0xef, 0x02, 0x93, 0x98, 0x27, 0x7e, 0x81, 0x21, 0x5d, 0x20, 0x9d, 0x32, 0x02,
+            0x21, 0x00, 0x8b, 0x6b, 0x49, 0xb6, 0x7d, 0x3e, 0x67, 0x9e, 0xb1, 0x22, 0xd3, 0x63, 0x82, 0x40, 0x4f, 0x49, 0xa4,
+            0xdc, 0x17, 0x35, 0xac, 0x4b, 0x7a, 0xbf, 0x52, 0x05, 0x58, 0x68, 0xe0, 0xaa, 0xd2, 0x8e,
+        };
+        const uint8_t kGoodCsrSubjectPublicKey[65] = {
+            0x04, 0xa3, 0xbe, 0xa1, 0xf5, 0x42, 0x01, 0x07, 0x3c, 0x4b, 0x75, 0x85, 0xd8, 0xe2, 0x98, 0xac, 0x2f,
+            0xf6, 0x98, 0xdb, 0xd9, 0x5b, 0xe0, 0x7e, 0xc1, 0x04, 0xd5, 0x73, 0xc5, 0xb0, 0x90, 0x77, 0x27, 0x00,
+            0x1e, 0x22, 0xc7, 0x89, 0x5e, 0x4d, 0x75, 0x07, 0x89, 0x82, 0x0f, 0x49, 0xb6, 0x59, 0xd5, 0xc5, 0x15,
+            0x7d, 0x93, 0xe6, 0x80, 0x5c, 0x70, 0x89, 0x0a, 0x43, 0x10, 0x3d, 0xeb, 0x3d, 0x4a,
+        };
+
+        Crypto::ClearSecretData(pubKey.Bytes(), pubKey.Length());
+
+        err = VerifyCertificateSigningRequestFormat(&kGoodCsr[0], sizeof(kGoodCsr));
+        NL_TEST_ASSERT(inSuite, err == CHIP_NO_ERROR);
+
+        err = VerifyCertificateSigningRequest(&kGoodCsr[0], sizeof(kGoodCsr), pubKey);
+        NL_TEST_ASSERT(inSuite, err == CHIP_NO_ERROR);
+
+        Crypto::P256PublicKey expected(kGoodCsrSubjectPublicKey);
+        NL_TEST_ASSERT(inSuite, pubKey.Matches(expected));
+    }
+
+    // Third case: bad signature
+    {
+        const uint8_t kBadSignatureSignatureCsr[205] = {
+            0x30, 0x81, 0xca, 0x30, 0x70, 0x02, 0x01, 0x00, 0x30, 0x0e, 0x31, 0x0c, 0x30, 0x0a, 0x06, 0x03, 0x55, 0x04, 0x0a,
+            0x0c, 0x03, 0x43, 0x53, 0x52, 0x30, 0x59, 0x30, 0x13, 0x06, 0x07, 0x2a, 0x86, 0x48, 0xce, 0x3d, 0x02, 0x01, 0x06,
+            0x08, 0x2a, 0x86, 0x48, 0xce, 0x3d, 0x03, 0x01, 0x07, 0x03, 0x42, 0x00, 0x04, 0xa3, 0xbe, 0xa1, 0xf5, 0x42, 0x01,
+            0x07, 0x3c, 0x4b, 0x75, 0x85, 0xd8, 0xe2, 0x98, 0xac, 0x2f, 0xf6, 0x98, 0xdb, 0xd9, 0x5b, 0xe0, 0x7e, 0xc1, 0x04,
+            0xd5, 0x73, 0xc5, 0xb0, 0x90, 0x77, 0x27, 0x00, 0x1e, 0x22, 0xc7, 0x89, 0x5e, 0x4d, 0x75, 0x07, 0x89, 0x82, 0x0f,
+            0x49, 0xb6, 0x59, 0xd5, 0xc5, 0x15, 0x7d, 0x93, 0xe6, 0x80, 0x5c, 0x70, 0x89, 0x0a, 0x43, 0x10, 0x3d, 0xeb, 0x3d,
+            0x4a, 0xa0, 0x00, 0x30, 0x0c, 0x06, 0x08, 0x2a, 0x86, 0x48, 0xce, 0x3d, 0x04, 0x03, 0x02, 0x05, 0x00, 0x03, 0x48,
+            0x00, 0x30, 0x45, 0x02, 0x20, 0x1d, 0x86, 0x21, 0xb4, 0xc2, 0xe1, 0xa9, 0xf3, 0xbc, 0xc8, 0x7c, 0xda, 0xb4, 0xb9,
+            0xc6, 0x8c, 0xd0, 0xe4, 0x9a, 0x9c, 0xef, 0x02, 0x93, 0x98, 0x27, 0x7e, 0x81, 0x21, 0x5d, 0x20, 0x9d, 0x32, 0x02,
+            0x21, 0x00, 0x8b, 0x6b, 0x49, 0xb6, 0x7d, 0x3e, 0x67, 0x9e, 0xb1, 0x21, 0xd3, 0x63, 0x82, 0x40, 0x4f, 0x49, 0xa4,
+            0xdc, 0x17, 0x35, 0xac, 0x4b, 0x7a, 0xbf, 0x52, 0x05, 0x58, 0x68, 0xe0, 0xaa, 0xd2, 0x8e,
+        };
+
+        Crypto::ClearSecretData(pubKey.Bytes(), pubKey.Length());
+
+        err = VerifyCertificateSigningRequestFormat(&kBadSignatureSignatureCsr[0], sizeof(kBadSignatureSignatureCsr));
+        NL_TEST_ASSERT(inSuite, err == CHIP_NO_ERROR);
+
+        err = VerifyCertificateSigningRequest(&kBadSignatureSignatureCsr[0], sizeof(kBadSignatureSignatureCsr), pubKey);
+        NL_TEST_ASSERT(inSuite, err != CHIP_NO_ERROR);
+    }
+
+    // Fourth case: CSR too big
+    {
+        const uint8_t kBadTooBigCsr[256] = {
+            0x30, 0x81, 0xda, 0x30, 0x81, 0x81, 0x02, 0x01, 0x00, 0x30, 0x0e, 0x31, 0x0c, 0x30, 0x0a, 0x06, 0x03, 0x55, 0x04, 0x0b,
+            0x0c, 0x03, 0x43, 0x53, 0x41, 0x30, 0x59, 0x30, 0x13, 0x06, 0x07, 0x2a, 0x86, 0x48, 0xce, 0x3d, 0x02, 0x01, 0x06, 0x08,
+            0x2a, 0x86, 0x48, 0xce, 0x3d, 0x03, 0x01, 0x07, 0x03, 0x42, 0x00, 0x04, 0x72, 0x48, 0xc0, 0x36, 0xf0, 0x12, 0x5f, 0xd1,
+            0x68, 0x92, 0x2d, 0xee, 0x57, 0x2b, 0x8e, 0x20, 0x9d, 0x97, 0xfa, 0x73, 0x92, 0xf1, 0xa0, 0x91, 0x0e, 0xfd, 0x04, 0x93,
+            0x66, 0x47, 0x3c, 0xa3, 0xf0, 0xa8, 0x47, 0xa1, 0xa3, 0x1e, 0x13, 0x3b, 0x67, 0x3b, 0x18, 0xca, 0x77, 0xd1, 0xea, 0xe3,
+            0x74, 0x93, 0x49, 0x8b, 0x9d, 0xdc, 0xef, 0xf9, 0xd5, 0x9b, 0x27, 0x19, 0xad, 0x6e, 0x90, 0xd2, 0xa0, 0x11, 0x30, 0x0f,
+            0x06, 0x09, 0x2a, 0x86, 0x48, 0x86, 0xf7, 0x0d, 0x01, 0x09, 0x0e, 0x31, 0x02, 0x30, 0x00, 0x30, 0x0a, 0x06, 0x08, 0x2a,
+            0x86, 0x48, 0xce, 0x3d, 0x04, 0x03, 0x02, 0x03, 0x48, 0x00, 0x30, 0x45, 0x02, 0x20, 0x6a, 0x2e, 0x15, 0x34, 0x1b, 0xde,
+            0xcb, 0x8f, 0xd2, 0xfd, 0x35, 0x03, 0x89, 0x0e, 0xed, 0x23, 0x54, 0xff, 0xcb, 0x79, 0xf9, 0xcb, 0x40, 0x33, 0x59, 0xb4,
+            0x27, 0x69, 0xeb, 0x07, 0x3b, 0xd5, 0x02, 0x21, 0x00, 0xb0, 0x25, 0xc9, 0xc2, 0x21, 0xe8, 0x54, 0xcc, 0x08, 0x12, 0xf5,
+            0x10, 0x3a, 0x0b, 0x25, 0x20, 0x0a, 0x61, 0x38, 0xc8, 0x6f, 0x82, 0xa7, 0x51, 0x84, 0x61, 0xae, 0x93, 0x69, 0xe4, 0x74,
+            0x84, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
+            0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x01,
+        };
+
+        Crypto::ClearSecretData(pubKey.Bytes(), pubKey.Length());
+        err = VerifyCertificateSigningRequestFormat(&kBadTooBigCsr[0], sizeof(kBadTooBigCsr));
+        NL_TEST_ASSERT(inSuite, err == CHIP_ERROR_UNSUPPORTED_CERT_FORMAT);
+
+        err = VerifyCertificateSigningRequest(&kBadTooBigCsr[0], sizeof(kBadTooBigCsr), pubKey);
+        NL_TEST_ASSERT(inSuite, err != CHIP_NO_ERROR);
+    }
+
+    // Fifth case: obviously invalid CSR (1/2)
+    {
+        const uint8_t kTooSmallCsr[10] = { 0x30, 0x81, 0xda, 0x30, 0x81, 0x81, 0x02, 0x01, 0x00, 0x30 };
+
+        Crypto::ClearSecretData(pubKey.Bytes(), pubKey.Length());
+
+        err = VerifyCertificateSigningRequestFormat(&kTooSmallCsr[0], sizeof(kTooSmallCsr));
+        NL_TEST_ASSERT(inSuite, err == CHIP_ERROR_UNSUPPORTED_CERT_FORMAT);
+
+        err = VerifyCertificateSigningRequest(&kTooSmallCsr[0], sizeof(kTooSmallCsr), pubKey);
+        NL_TEST_ASSERT(inSuite, err != CHIP_NO_ERROR);
+    }
+
+    // Sixth case: obviously invalid CSR (2/2)
+    {
+        const uint8_t kNotSequenceCsr[205] = {
+            0x31, 0x81, 0xca, 0x30, 0x70, 0x02, 0x01, 0x00, 0x30, 0x0e, 0x31, 0x0c, 0x30, 0x0a, 0x06, 0x03, 0x55, 0x04, 0x0a,
+            0x0c, 0x03, 0x43, 0x53, 0x52, 0x30, 0x59, 0x30, 0x13, 0x06, 0x07, 0x2a, 0x86, 0x48, 0xce, 0x3d, 0x02, 0x01, 0x06,
+            0x08, 0x2a, 0x86, 0x48, 0xce, 0x3d, 0x03, 0x01, 0x07, 0x03, 0x42, 0x00, 0x04, 0xa3, 0xbe, 0xa1, 0xf5, 0x42, 0x01,
+            0x07, 0x3c, 0x4b, 0x75, 0x85, 0xd8, 0xe2, 0x98, 0xac, 0x2f, 0xf6, 0x98, 0xdb, 0xd9, 0x5b, 0xe0, 0x7e, 0xc1, 0x04,
+            0xd5, 0x73, 0xc5, 0xb0, 0x90, 0x77, 0x27, 0x00, 0x1e, 0x22, 0xc7, 0x89, 0x5e, 0x4d, 0x75, 0x07, 0x89, 0x82, 0x0f,
+            0x49, 0xb6, 0x59, 0xd5, 0xc5, 0x15, 0x7d, 0x93, 0xe6, 0x80, 0x5c, 0x70, 0x89, 0x0a, 0x43, 0x10, 0x3d, 0xeb, 0x3d,
+            0x4a, 0xa0, 0x00, 0x30, 0x0c, 0x06, 0x08, 0x2a, 0x86, 0x48, 0xce, 0x3d, 0x04, 0x03, 0x02, 0x05, 0x00, 0x03, 0x48,
+            0x00, 0x30, 0x45, 0x02, 0x20, 0x1d, 0x86, 0x21, 0xb4, 0xc2, 0xe1, 0xa9, 0xf3, 0xbc, 0xc8, 0x7c, 0xda, 0xb4, 0xb9,
+            0xc6, 0x8c, 0xd0, 0xe4, 0x9a, 0x9c, 0xef, 0x02, 0x93, 0x98, 0x27, 0x7e, 0x81, 0x21, 0x5d, 0x20, 0x9d, 0x32, 0x02,
+            0x21, 0x00, 0x8b, 0x6b, 0x49, 0xb6, 0x7d, 0x3e, 0x67, 0x9e, 0xb1, 0x22, 0xd3, 0x63, 0x82, 0x40, 0x4f, 0x49, 0xa4,
+            0xdc, 0x17, 0x35, 0xac, 0x4b, 0x7a, 0xbf, 0x52, 0x05, 0x58, 0x68, 0xe0, 0xaa, 0xd2, 0x8e,
+        };
+
+        Crypto::ClearSecretData(pubKey.Bytes(), pubKey.Length());
+
+        err = VerifyCertificateSigningRequestFormat(&kNotSequenceCsr[0], sizeof(kNotSequenceCsr));
+        NL_TEST_ASSERT(inSuite, err == CHIP_ERROR_UNSUPPORTED_CERT_FORMAT);
+
+        err = VerifyCertificateSigningRequest(&kNotSequenceCsr[0], sizeof(kNotSequenceCsr), pubKey);
+        NL_TEST_ASSERT(inSuite, err != CHIP_NO_ERROR);
+    }
+}
+
 void TestCSR_GenDirect(nlTestSuite * inSuite, void * inContext)
 {
     uint8_t csrBuf[kMAX_CSR_Length];
@@ -2136,6 +2300,7 @@ static const nlTest sTests[] = {
     NL_TEST_DEF("Test adding entropy sources", TestAddEntropySources),
     NL_TEST_DEF("Test PBKDF2 SHA256", TestPBKDF2_SHA256_TestVectors),
     NL_TEST_DEF("Test P256 Keygen", TestP256_Keygen),
+    NL_TEST_DEF("Test CSR Verification + PK extraction", TestCSR_Verify),
     NL_TEST_DEF("Test CSR Generation via P256Keypair method", TestCSR_GenByKeypair),
     NL_TEST_DEF("Test Direct CSR Generation", TestCSR_GenDirect),
     NL_TEST_DEF("Test Keypair Serialize", TestKeypair_Serialize),

src/platform/EFR32/CHIPCryptoPALPsaEfr32.cpp

@@ -902,6 +902,8 @@ CHIP_ERROR P256Keypair::NewCertificateSigningRequest(uint8_t * out_csr, size_t &
 CHIP_ERROR VerifyCertificateSigningRequest(const uint8_t * csr_buf, size_t csr_length, P256PublicKey & pubkey)
 {
 #if defined(MBEDTLS_X509_CSR_PARSE_C)
+    ReturnErrorOnFailure(VerifyCertificateSigningRequestFormat(csr_buf, csr_length));
+
     // TODO: For some embedded targets, mbedTLS library doesn't have mbedtls_x509_csr_parse_der, and mbedtls_x509_csr_parse_free.
     //       Taking a step back, embedded targets likely will not process CSR requests. Adding this action item to reevaluate
     //       this if there's a need for this processing for embedded targets.