test DNS name constraints on CA are applied against Subject CN name when SAN name is unavailable

Author: rlm2002

tests/api/test_certman.c

@@ -1584,6 +1584,101 @@ int test_wolfSSL_CertManagerNameConstraint5(void)
     return EXPECT_RESULT();
 }
 
+int test_wolfSSL_CertManagerNameConstraint_DNS_CN(void)
+{
+    EXPECT_DECLS;
+#if !defined(NO_FILESYSTEM) && !defined(NO_CERTS) && \
+    !defined(NO_WOLFSSL_CM_VERIFY) && !defined(NO_RSA) && \
+    defined(OPENSSL_EXTRA) && defined(WOLFSSL_CERT_GEN) && \
+    defined(WOLFSSL_CERT_EXT) && defined(WOLFSSL_ALT_NAMES) && \
+    !defined(NO_SHA256)
+    /* Test that DNS name constraints are enforced against the Subject CN
+     * when no SAN extension is present. The CA cert (cert-ext-ncdns.der)
+     * permits only DNS:wolfssl.com and DNS:example.com. A leaf cert with
+     * CN=evil.attacker.com and no SAN should be REJECTED. */
+    WOLFSSL_CERT_MANAGER* cm = NULL;
+    WOLFSSL_EVP_PKEY *priv = NULL;
+    WOLFSSL_X509_NAME* name = NULL;
+    const char* ca_cert = "./certs/test/cert-ext-ncdns.der";
+    const char* server_cert = "./certs/test/server-goodcn.pem";
+
+    byte    *der = NULL;
+    int     derSz;
+    byte    *pt;
+    WOLFSSL_X509 *x509 = NULL;
+    WOLFSSL_X509 *ca = NULL;
+
+    pt = (byte*)server_key_der_2048;
+    ExpectNotNull(priv = wolfSSL_d2i_PrivateKey(EVP_PKEY_RSA, NULL,
+                (const unsigned char**)&pt, sizeof_server_key_der_2048));
+
+    ExpectNotNull(cm = wolfSSL_CertManagerNew());
+    ExpectNotNull(ca = wolfSSL_X509_load_certificate_file(ca_cert,
+                WOLFSSL_FILETYPE_ASN1));
+    ExpectNotNull((der = (byte*)wolfSSL_X509_get_der(ca, &derSz)));
+    ExpectIntEQ(wolfSSL_CertManagerLoadCABuffer(cm, der, derSz,
+                WOLFSSL_FILETYPE_ASN1), WOLFSSL_SUCCESS);
+
+    /* Sanity check: cert with SAN=evil.attacker.com is correctly rejected */
+    ExpectNotNull(x509 = wolfSSL_X509_load_certificate_file(server_cert,
+                WOLFSSL_FILETYPE_PEM));
+    ExpectNotNull(name = wolfSSL_X509_get_subject_name(ca));
+    ExpectIntEQ(wolfSSL_X509_set_issuer_name(x509, name), WOLFSSL_SUCCESS);
+    name = NULL;
+
+    ExpectNotNull(name = X509_NAME_new());
+    ExpectIntEQ(X509_NAME_add_entry_by_txt(name, "countryName", MBSTRING_UTF8,
+                                       (byte*)"US", 2, -1, 0), SSL_SUCCESS);
+    ExpectIntEQ(X509_NAME_add_entry_by_txt(name, "commonName", MBSTRING_UTF8,
+                             (byte*)"evil.attacker.com", 17, -1, 0),
+                SSL_SUCCESS);
+    ExpectIntEQ(wolfSSL_X509_set_subject_name(x509, name), WOLFSSL_SUCCESS);
+    X509_NAME_free(name);
+    name = NULL;
+
+    ExpectIntEQ(wolfSSL_X509_add_altname(x509, "evil.attacker.com",
+                                         ASN_DNS_TYPE), WOLFSSL_SUCCESS);
+    ExpectIntGT(wolfSSL_X509_sign(x509, priv, EVP_sha256()), 0);
+    ExpectNotNull((der = (byte*)wolfSSL_X509_get_der(x509, &derSz)));
+    ExpectIntEQ(wolfSSL_CertManagerVerifyBuffer(cm, der, derSz,
+                WOLFSSL_FILETYPE_ASN1), WC_NO_ERR_TRACE(ASN_NAME_INVALID_E));
+    wolfSSL_X509_free(x509);
+    x509 = NULL;
+
+    /* NOW the actual vulnerability test: cert with CN=evil.attacker.com
+     * but NO SAN. The DNS name constraint should still reject this, since
+     * wolfSSL's hostname verification falls back to CN when no SAN exists. */
+    ExpectNotNull(x509 = wolfSSL_X509_load_certificate_file(server_cert,
+                WOLFSSL_FILETYPE_PEM));
+    ExpectNotNull(name = wolfSSL_X509_get_subject_name(ca));
+    ExpectIntEQ(wolfSSL_X509_set_issuer_name(x509, name), WOLFSSL_SUCCESS);
+    name = NULL;
+
+    ExpectNotNull(name = X509_NAME_new());
+    ExpectIntEQ(X509_NAME_add_entry_by_txt(name, "countryName", MBSTRING_UTF8,
+                                       (byte*)"US", 2, -1, 0), SSL_SUCCESS);
+    ExpectIntEQ(X509_NAME_add_entry_by_txt(name, "commonName", MBSTRING_UTF8,
+                             (byte*)"evil.attacker.com", 17, -1, 0),
+                SSL_SUCCESS);
+    ExpectIntEQ(wolfSSL_X509_set_subject_name(x509, name), WOLFSSL_SUCCESS);
+    X509_NAME_free(name);
+    name = NULL;
+
+    /* Do NOT add any SAN — this is the bypass vector */
+    ExpectIntGT(wolfSSL_X509_sign(x509, priv, EVP_sha256()), 0);
+    ExpectNotNull((der = (byte*)wolfSSL_X509_get_der(x509, &derSz)));
+    /* Should be ASN_NAME_INVALID_E because CN violates the constraint */
+    ExpectIntEQ(wolfSSL_CertManagerVerifyBuffer(cm, der, derSz,
+                WOLFSSL_FILETYPE_ASN1), WC_NO_ERR_TRACE(ASN_NAME_INVALID_E));
+
+    wolfSSL_CertManagerFree(cm);
+    wolfSSL_X509_free(x509);
+    wolfSSL_X509_free(ca);
+    wolfSSL_EVP_PKEY_free(priv);
+#endif
+    return EXPECT_RESULT();
+}
+
 int test_wolfSSL_CertManagerCRL(void)
 {
     EXPECT_DECLS;

tests/api/test_certman.h

@@ -35,6 +35,7 @@ int test_wolfSSL_CertManagerNameConstraint2(void);
 int test_wolfSSL_CertManagerNameConstraint3(void);
 int test_wolfSSL_CertManagerNameConstraint4(void);
 int test_wolfSSL_CertManagerNameConstraint5(void);
+int test_wolfSSL_CertManagerNameConstraint_DNS_CN(void);
 int test_wolfSSL_CertManagerCRL(void);
 int test_wolfSSL_CRL_reason_extensions_cleanup(void);
 int test_wolfSSL_CRL_static_revoked_list(void);
@@ -54,6 +55,7 @@ int test_various_pathlen_chains(void);
     TEST_DECL_GROUP("certman", test_wolfSSL_CertManagerNameConstraint3),    \
     TEST_DECL_GROUP("certman", test_wolfSSL_CertManagerNameConstraint4),    \
     TEST_DECL_GROUP("certman", test_wolfSSL_CertManagerNameConstraint5),    \
+    TEST_DECL_GROUP("certman", test_wolfSSL_CertManagerNameConstraint_DNS_CN), \
     TEST_DECL_GROUP("certman", test_wolfSSL_CertManagerCRL),                \
     TEST_DECL_GROUP("certman", test_wolfSSL_CRL_reason_extensions_cleanup), \
     TEST_DECL_GROUP("certman", test_wolfSSL_CRL_static_revoked_list),      \