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DNS name constraint fix #10837

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9a0a01a
Apply Subject CN dNSName name-constraint check unless a dNSName SAN i…
rlm2002 Jul 2, 2026
bd4c11a
Expand test_wolfSSL_CertManagerNameConstraint_DNS_CN with non-dNSName…
rlm2002 Jul 2, 2026
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126 changes: 113 additions & 13 deletions tests/api/test_certman.c
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Original file line number Diff line number Diff line change
Expand Up @@ -1591,16 +1591,20 @@ int test_wolfSSL_CertManagerNameConstraint_DNS_CN(void)
!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. */
!defined(NO_SHA256) && !defined(IGNORE_NAME_CONSTRAINTS)
/* CA (cert-ext-ncdns.der) permits DNS:wolfssl.com and DNS:example.com. The
* Subject CN is checked against these dNSName constraints as a fallback
* only when the leaf has no dNSName SAN (RFC 6125 6.4.4); a non-dNSName
* SAN must not suppress that check. */
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";
/* non-dNSName SAN values. The CA declares no registeredID or iPAddress
* constraint, so these names are themselves unconstrained. */
static const byte rid_dummy[] = { 0x2A, 0x03, 0x04 }; /* OID 1.2.3.4 */
static const byte ip_dummy[] = { 203, 0, 113, 7 };

byte *der = NULL;
int derSz;
Expand All @@ -1619,7 +1623,7 @@ int test_wolfSSL_CertManagerNameConstraint_DNS_CN(void)
ExpectIntEQ(wolfSSL_CertManagerLoadCABuffer(cm, der, derSz,
WOLFSSL_FILETYPE_ASN1), WOLFSSL_SUCCESS);

/* Sanity check: cert with SAN=evil.attacker.com is correctly rejected */
/* Negative case: leaf with an out-of-scope dNSName SAN. */
ExpectNotNull(x509 = wolfSSL_X509_load_certificate_file(server_cert,
WOLFSSL_FILETYPE_PEM));
ExpectNotNull(name = wolfSSL_X509_get_subject_name(ca));
Expand All @@ -1645,9 +1649,33 @@ int test_wolfSSL_CertManagerNameConstraint_DNS_CN(void)
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. */
/* Positive case: leaf with an out-of-scope CN but an in-scope dNSName
* SAN; the dNSName SAN suppresses the CN fallback, so it is accepted. */
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, "wolfssl.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), WOLFSSL_SUCCESS);
wolfSSL_X509_free(x509);
x509 = NULL;

/* Negative case: leaf with an out-of-scope CN and no SAN; the CN is
* checked against the DNS constraint as a fallback. */
ExpectNotNull(x509 = wolfSSL_X509_load_certificate_file(server_cert,
WOLFSSL_FILETYPE_PEM));
ExpectNotNull(name = wolfSSL_X509_get_subject_name(ca));
Expand All @@ -1664,17 +1692,15 @@ int test_wolfSSL_CertManagerNameConstraint_DNS_CN(void)
X509_NAME_free(name);
name = NULL;

/* Do NOT add any SAN this is the bypass vector */
/* No SAN added; CN=evil.attacker.com violates the DNS constraint. */
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_X509_free(x509);
x509 = NULL;

/* Positive test: CN matches a permitted name (wolfssl.com) and no SAN is
* present. The CN fallback should accept this cert. */
/* Positive case: leaf with an in-scope CN and no SAN. */
ExpectNotNull(x509 = wolfSSL_X509_load_certificate_file(server_cert,
WOLFSSL_FILETYPE_PEM));
ExpectNotNull(name = wolfSSL_X509_get_subject_name(ca));
Expand All @@ -1694,6 +1720,80 @@ int test_wolfSSL_CertManagerNameConstraint_DNS_CN(void)
/* No SAN added; CN=wolfssl.com matches the permitted DNS constraint. */
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), WOLFSSL_SUCCESS);
wolfSSL_X509_free(x509);
x509 = NULL;

/* Negative case: leaf with an out-of-scope CN and a registeredID SAN;
* a non-dNSName SAN must not suppress the CN check. */
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_ex(x509, (const char*)rid_dummy,
sizeof(rid_dummy), ASN_RID_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;

/* Negative case: leaf with an out-of-scope CN and an iPAddress SAN. */
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_ex(x509, (const char*)ip_dummy,
sizeof(ip_dummy), ASN_IP_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;

/* Positive case: leaf with an in-scope CN and a registeredID SAN; the
* check must not over-reject. */
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*)"wolfssl.com", 11, -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_ex(x509, (const char*)rid_dummy,
sizeof(rid_dummy), ASN_RID_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), WOLFSSL_SUCCESS);

Expand Down
26 changes: 18 additions & 8 deletions wolfcrypt/src/asn.c
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Original file line number Diff line number Diff line change
Expand Up @@ -18748,20 +18748,30 @@ static int ConfirmNameConstraints(Signer* signer, DecodedCert* cert)
byte nameType = nameTypes[i];
DNS_entry* name = NULL;
DNS_entry subjectDnsName; /* temporary node used for subject name */
DNS_entry* dnsSan = NULL; /* scan for a dNSName SAN */

XMEMSET(&subjectDnsName, 0, sizeof(DNS_entry));
switch (nameType) {
case ASN_DNS_TYPE:
name = cert->altNames;

/* Apply DNS constraints to leaf Subject CN when no SAN
* (legacy hostname-in-CN). Skipped for CAs. */
if (cert->subjectCN != NULL && cert->altNames == NULL &&
!cert->isCA) {
subjectDnsName.next = NULL;
subjectDnsName.type = ASN_DNS_TYPE;
subjectDnsName.len = cert->subjectCNLen;
subjectDnsName.name = cert->subjectCN;
/* Apply DNS name constraints to the Subject CN as a legacy
* hostname-in-CN fallback only when the cert presents no
* dNSName SAN (RFC 6125 6.4.4). A SAN of another type
* (iPAddress/registeredID/otherName/...) must NOT suppress
* this check. Skip for CA certs. */
if (cert->subjectCN != NULL && !cert->isCA) {
for (dnsSan = cert->altNames; dnsSan != NULL;
dnsSan = dnsSan->next) {
if (dnsSan->type == ASN_DNS_TYPE)
break;
}
if (dnsSan == NULL) { /* no dNSName SAN present */
subjectDnsName.next = NULL;
subjectDnsName.type = ASN_DNS_TYPE;
subjectDnsName.len = cert->subjectCNLen;
subjectDnsName.name = cert->subjectCN;
}
}
break;
case ASN_IP_TYPE:
Expand Down
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