CVE-2017-7524 (C, published 2017-06-27T14:29Z)
Description: value: tpm2-tools versions before 1.1.1 are vulnerable to a password leak due to transmitting password in plaintext from client to server when generating HMAC.
Severity: MEDIUM (CVSS v3 base score: 7.5)
Weakness: CWE-522 \u2014 Insufficiently Protected Credentials
The product transmits or stores authentication credentials, but it uses an insecure method that is susceptible to unauthorized interception and/or retrieval.
Repository: https://github.com/01org/tpm2.0-tools
Files changed:
Makefile.am
configure.ac
lib/tpm_kdfa.c
lib/tpm_kdfa.h
lib/tpm_session.c
Commit message: kdfa: use openssl for hmac not tpm

While not reachable in the current code base tools, a potential
security bug lurked in tpm_kdfa().

If using that routine for an hmac authorization, the hmac was
calculated using the tpm. A user of an object wishing to
authenticate via hmac, would expect that the password is never
sent to the tpm. However, since the hmac calculation relies on
password, and is performed by the tpm, the password ends up
being sent in plain text to the tpm.

The fix is to use openssl to generate the hmac on the host.

Fixes: CVE-2017-7524

Signed-off-by: William Roberts <william.c.roberts@intel.com>


Vulnerable code:
AM_CFLAGS    := $(INCLUDE_DIRS) $(TPM20_TSS_CFLAGS) $(EXTRA_CFLAGS) $(TCTI_TABRMD_CFLAGS)
LDADD = $(LIB_COMMON) $(TPM20_TSS_LIBS) $(TCTI_SOCK_LIBS) $(TCTI_DEV_LIBS) $(TCTI_TABRMD_LIBS)
PKG_CHECK_MODULES([CURL],[libcurl libcrypto])
TPM_RC tpm_kdfa(TSS2_SYS_CONTEXT *sapi_context, TPMI_ALG_HASH hashAlg,
    TPM2B_DIGEST tmpResult;
    TPM_RC rval;
        bufferList[j++] = (TPM2B_DIGEST *)0;
        rval = tpm_hmac(sapi_context, hashAlg, key, (TPM2B **)&( bufferList[0] ), &tmpResult );
        if( rval != TPM_RC_SUCCESS )
        {
            return( rval );
            return TSS2_SYS_RC_BAD_VALUE;
    return TPM_RC_SUCCESS;
TPM_RC tpm_kdfa(TSS2_SYS_CONTEXT *sapi_context, TPMI_ALG_HASH hashAlg,
                rval = tpm_kdfa(sapi_context, session->authHash, &(key.b), label, &( session->nonceNewer.b ),

Fixed code:
AM_CFLAGS    := $(INCLUDE_DIRS) $(TPM20_TSS_CFLAGS) $(EXTRA_CFLAGS) $(TCTI_TABRMD_CFLAGS) $(CRYPTO_CFLAGS)
LDADD = $(LIB_COMMON) $(TPM20_TSS_LIBS) $(TCTI_SOCK_LIBS) $(TCTI_DEV_LIBS) $(TCTI_TABRMD_LIBS) $(CRYPTO_LIBS)
PKG_CHECK_MODULES([CRYPTO],[libcrypto])
PKG_CHECK_MODULES([CURL],[libcurl])
 #include <openssl/err.h>
#include <openssl/hmac.h>

#include "log.h"

static const EVP_MD *tpm_algorithm_to_openssl_digest(TPMI_ALG_HASH algorithm) {

    switch(algorithm) {
    case TPM_ALG_SHA1:
        return EVP_sha1();
    case ALG_SHA256_VALUE:
        return EVP_sha256();
    case TPM_ALG_SHA384:
        return EVP_sha384();
    case TPM_ALG_SHA512:
        return EVP_sha512();
    default:
        return NULL;
    }
    /* no return, not possible */
}
TPM_RC tpm_kdfa(TPMI_ALG_HASH hashAlg,
    TPM_RC rval = TPM_RC_SUCCESS;
    const EVP_MD *md = tpm_algorithm_to_openssl_digest(hashAlg);
    if (!md) {
        LOG_ERR("Algorithm not supported for hmac: %x", hashAlg);
        return TPM_RC_HASH;
    }

    HMAC_CTX ctx;
    HMAC_CTX_init(&ctx);
    int rc = HMAC_Init_ex(&ctx, key->buffer, key->size, md, NULL);
    if (!rc) {
        LOG_ERR("HMAC Init failed: %s", ERR_error_string(rc, NULL));
        return TPM_RC_MEMORY;
    }

    // TODO Why is this a loop? It appears to only execute once.
        TPM2B_DIGEST tmpResult;
        bufferList[j] = (TPM2B_DIGEST *)0;

        int c;
        for(c=0; c < j; c++) {
            TPM2B_DIGEST *digest = bufferList[c];
            int rc =  HMAC_Update(&ctx, digest->b.buffer, digest->b.size);
            if (!rc) {
                LOG_ERR("HMAC Update failed: %s", ERR_error_string(rc, NULL));
                rval = TPM_RC_MEMORY;
                goto err;
            }
        }

        unsigned size = sizeof(tmpResult.t.buffer);
        int rc = HMAC_Final(&ctx, tmpResult.t.buffer, &size);
        if (!rc) {
            LOG_ERR("HMAC Final failed: %s", ERR_error_string(rc, NULL));
            rval = TPM_RC_MEMORY;
            goto err;
        tmpResult.t.size = size;

            rval = TSS2_SYS_RC_BAD_VALUE;
            goto err;
err:
    HMAC_CTX_cleanup(&ctx);

    return rval;
TPM_RC tpm_kdfa(TPMI_ALG_HASH hashAlg,
                rval = tpm_kdfa(session->authHash, &(key.b), label, &( session->nonceNewer.b ),