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certman: enforce leaf is end-entity in VerifyCerts_buffer #1075

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certman: enforce leaf is end-entity in VerifyCerts_buffer #1075

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102 changes: 69 additions & 33 deletions src/certman.c
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Original file line number Diff line number Diff line change
Expand Up @@ -208,22 +208,42 @@ enum {
static int CertManIntermediateIsCA(WOLFSSH_CERTMAN* cm,
const unsigned char* der, word32 derSz)
{
DecodedCert decoded;
DecodedCert* decoded = NULL;
#ifndef WOLFSSH_SMALL_STACK
DecodedCert decoded_s;
#endif
int isCA = 0;

wc_InitDecodedCert(&decoded, der, derSz, cm->heap);
if (wc_ParseCert(&decoded, WOLFSSL_FILETYPE_ASN1, NO_VERIFY, NULL) == 0) {
isCA = decoded.isCA;
#ifndef ALLOW_INVALID_CERTSIGN
if (isCA && !decoded.selfSigned && decoded.extKeyUsageSet &&
(decoded.extKeyUsage & KEYUSE_KEY_CERT_SIGN) == 0) {
/* If a KeyUsage extension is present, an intermediate CA must
* assert the keyCertSign bit. */
isCA = 0;
#ifndef WOLFSSH_SMALL_STACK
decoded = &decoded_s;
#else
decoded = (DecodedCert*)WMALLOC(sizeof(DecodedCert), cm->heap,
DYNTYPE_CERT);
#endif

if (decoded != NULL) {
wc_InitDecodedCert(decoded, der, derSz, cm->heap);
if (wc_ParseCert(decoded, WOLFSSL_FILETYPE_ASN1, NO_VERIFY, NULL) == 0) {
isCA = decoded->isCA;
#ifndef ALLOW_INVALID_CERTSIGN
if (isCA && !decoded->selfSigned && decoded->extKeyUsageSet &&
(decoded->extKeyUsage & KEYUSE_KEY_CERT_SIGN) == 0) {
/* If a KeyUsage extension is present, an intermediate CA must
* assert the keyCertSign bit. */
isCA = 0;
}
#endif
}
wc_FreeDecodedCert(decoded);
#ifdef WOLFSSH_SMALL_STACK
WFREE(decoded, cm->heap, DYNTYPE_CERT);
#endif
}
wc_FreeDecodedCert(&decoded);
else {
/* allocation failed; fail closed (not a CA) but log the real cause so
* it is not mistaken for a genuine non-CA intermediate */
WLOG(WS_LOG_CERTMAN, "could not allocate cert to check intermediate CA");
}

return isCA;
}
Expand Down Expand Up @@ -364,32 +384,51 @@ int wolfSSH_CERTMAN_VerifyCerts_buffer(WOLFSSH_CERTMAN* cm,
}
}

#ifndef WOLFSSH_NO_FPKI
/* FPKI checking on the leaf certificate */
/* Leaf (index 0) must be an end-entity cert; reject a CA leaf even without
* FPKI, and match a profile when FPKI is on. cm->cm resolves the signer
* (ca) that CheckProfile needs for the issuer-DN match. */
if (ret == WS_SUCCESS) {
DecodedCert decoded;
DecodedCert* decoded = NULL;
#ifndef WOLFSSH_SMALL_STACK
DecodedCert decoded_s;

wc_InitDecodedCert(&decoded, certLoc[0], certLen[0], cm->cm);
ret = wc_ParseCert(&decoded, WOLFSSL_FILETYPE_ASN1, 0, cm->cm);

if (ret == 0) {
ret =
CheckProfile(&decoded, PROFILE_FPKI_WORKSHEET_6) ||
CheckProfile(&decoded, PROFILE_FPKI_WORKSHEET_10) ||
CheckProfile(&decoded, PROFILE_FPKI_WORKSHEET_16);
decoded = &decoded_s;
#else
decoded = (DecodedCert*)WMALLOC(sizeof(DecodedCert), cm->heap,
DYNTYPE_CERT);
if (decoded == NULL) {
ret = WS_MEMORY_E;
}
#endif

if (ret == 0) {
WLOG(WS_LOG_CERTMAN, "certificate didn't match profile");
if (ret == WS_SUCCESS) {
wc_InitDecodedCert(decoded, certLoc[0], certLen[0], cm->heap);
if (wc_ParseCert(decoded, WOLFSSL_FILETYPE_ASN1, NO_VERIFY, cm->cm)
!= 0) {
WLOG(WS_LOG_CERTMAN, "unable to parse leaf certificate");
ret = WS_CERT_OTHER_E;
}
else if (decoded->isCA) {
WLOG(WS_LOG_CERTMAN, "leaf certificate is a CA; rejecting");
ret = WS_CERT_PROFILE_E;
}
else {
ret = WS_SUCCESS;
#ifndef WOLFSSH_NO_FPKI
else if (!(CheckProfile(decoded, PROFILE_FPKI_WORKSHEET_6) ||
CheckProfile(decoded, PROFILE_FPKI_WORKSHEET_10) ||
CheckProfile(decoded, PROFILE_FPKI_WORKSHEET_16))) {
WLOG(WS_LOG_CERTMAN, "certificate didn't match profile");
ret = WS_CERT_PROFILE_E;
}
#endif /* WOLFSSH_NO_FPKI */
wc_FreeDecodedCert(decoded);
}

FreeDecodedCert(&decoded);
#ifdef WOLFSSH_SMALL_STACK
if (decoded != NULL) {
WFREE(decoded, cm->heap, DYNTYPE_CERT);
}
#endif
}
#endif /* WOLFSSH_NO_FPKI */

if (certLoc != NULL)
WFREE(certLoc, cm->heap, DYNTYPE_CERT);
Expand Down Expand Up @@ -438,11 +477,8 @@ static int CheckProfile(DecodedCert* cert, int profile)
WLOG(WS_LOG_CERTMAN, "cert country of citizenship invalid");
}

if (valid) {
valid = !cert->isCA;
if (valid != 1)
WLOG(WS_LOG_CERTMAN, "cert basic constraint invalid");
}
/* leaf isCA (basic constraint) is enforced unconditionally by the caller
* before CheckProfile runs, so it is not re-checked here */

if (valid) {
valid =
Expand Down
89 changes: 89 additions & 0 deletions tests/api.c
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Original file line number Diff line number Diff line change
Expand Up @@ -701,6 +701,34 @@ static void test_wolfSSH_CTX_SetWindowPacketSize(void)
}


#if defined(WOLFSSH_CERTS) && !defined(WOLFSSH_NO_ECDSA)
/* Build the length-prefixed single-cert chain buffer that
* wolfSSH_CERTMAN_VerifyCerts_buffer expects. Caller frees *chain. */
static int certman_make_chain(const byte* cert, word32 certSz,
byte** chain, word32* chainSz)
{
int ret = 0;
byte* buf;

buf = (byte*)malloc(UINT32_SZ + certSz);
if (buf != NULL) {
buf[0] = (byte)(certSz >> 24);
buf[1] = (byte)(certSz >> 16);
buf[2] = (byte)(certSz >> 8);
buf[3] = (byte)(certSz);
memcpy(buf + UINT32_SZ, cert, certSz);
*chain = buf;
*chainSz = UINT32_SZ + certSz;
}
else {
ret = -1;
}

return ret;
}
#endif /* WOLFSSH_CERTS && !WOLFSSH_NO_ECDSA */


static void test_wolfSSH_CertMan(void)
{
#ifdef WOLFSSH_CERTMAN
Expand Down Expand Up @@ -751,6 +779,67 @@ static void test_wolfSSH_CertMan(void)

wolfSSH_CERTMAN_free(cm);
}
/* ECC trust anchor and leaf, so guard on ECDSA like the sibling tests. */
#ifndef WOLFSSH_NO_ECDSA
{
/* Negative control: a trusted CA presented as the leaf (index 0) must
* be rejected as an end-entity cert in both FPKI and non-FPKI builds;
* otherwise a trusted CA could be used to bypass authentication. */
WOLFSSH_CERTMAN* cm;
byte* caCert = NULL;
byte* chain = NULL;
word32 caCertSz = 0;
word32 chainSz;

cm = wolfSSH_CERTMAN_new(NULL);
AssertNotNull(cm);

AssertIntEQ(0, load_file("./keys/ca-cert-ecc.der", &caCert, &caCertSz));
AssertIntEQ(WS_SUCCESS,
wolfSSH_CERTMAN_LoadRootCA_buffer(cm, caCert, caCertSz));

AssertIntEQ(0, certman_make_chain(caCert, caCertSz, &chain, &chainSz));
AssertIntEQ(WS_CERT_PROFILE_E,
wolfSSH_CERTMAN_VerifyCerts_buffer(cm, chain, chainSz, 1));

free(chain);
free(caCert);
wolfSSH_CERTMAN_free(cm);
}
#ifdef WOLFSSH_NO_FPKI
{
/* Positive control: a genuine end-entity leaf signed by the CA still
* verifies. The leaf is not an FPKI cert, so only assert this when
* FPKI profile checking is compiled out. */
WOLFSSH_CERTMAN* cm;
byte* caCert = NULL;
byte* leafCert = NULL;
byte* chain = NULL;
word32 caCertSz = 0;
word32 leafCertSz = 0;
word32 chainSz;

cm = wolfSSH_CERTMAN_new(NULL);
AssertNotNull(cm);

AssertIntEQ(0, load_file("./keys/ca-cert-ecc.der", &caCert, &caCertSz));
AssertIntEQ(WS_SUCCESS,
wolfSSH_CERTMAN_LoadRootCA_buffer(cm, caCert, caCertSz));

AssertIntEQ(0,
load_file("./keys/fred-cert.der", &leafCert, &leafCertSz));
AssertIntEQ(0,
certman_make_chain(leafCert, leafCertSz, &chain, &chainSz));
AssertIntEQ(WS_SUCCESS,
wolfSSH_CERTMAN_VerifyCerts_buffer(cm, chain, chainSz, 1));

free(chain);
free(caCert);
free(leafCert);
wolfSSH_CERTMAN_free(cm);
}
#endif /* WOLFSSH_NO_FPKI */
#endif /* WOLFSSH_NO_ECDSA */
#endif /* WOLFSSH_CERTS */
}

Expand Down
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