CVE-2017-7524 (published 2017-06-27T14:29Z)

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 v2 base score: 5.0 (AV:N/AC:L/Au:N/C:P/I:N/A:N)
CVSS v3 base score: 7.5, HIGH (CVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N)

Weakness information:
cwe_id: CWE-522
cwe_name: Insufficiently Protected Credentials
description: The product transmits or stores authentication credentials, but it uses an insecure method that is susceptible to unauthorized interception and/or retrieval.
extended_description: 
            
            
            
         
         

Fix information:
repo_url: https://github.com/01org/tpm2.0-tools
commit_details: repo_url: https://github.com/01org/tpm2.0-tools
author: William Roberts
author_date: 2017-06-21 09:32:32-07:00
msg: 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>
repository: repo_url: https://github.com/01org/tpm2.0-tools
repo_name: tpm2-software/tpm2-tools
description: The source repository for the Trusted Platform Module (TPM2.0) tools
repo_language: C
owner: 01org
file_changes: filename: Makefile.am
change_type: ModificationType.MODIFY
diff: @@ -35,10 +35,10 @@ ACLOCAL_AMFLAGS = -I m4
 INCLUDE_DIRS = -I$(srcdir)/src -I$(srcdir)/lib
 LIB_COMMON := lib/libcommon.a
 
-AM_CFLAGS    := $(INCLUDE_DIRS) $(TPM20_TSS_CFLAGS) $(EXTRA_CFLAGS) $(TCTI_TABRMD_CFLAGS)
+AM_CFLAGS    := $(INCLUDE_DIRS) $(TPM20_TSS_CFLAGS) $(EXTRA_CFLAGS) $(TCTI_TABRMD_CFLAGS) $(CRYPTO_CFLAGS)
 AM_LDFLAGS   := $(EXTRA_LDFLAGS)
 
-LDADD = $(LIB_COMMON) $(TPM20_TSS_LIBS) $(TCTI_SOCK_LIBS) $(TCTI_DEV_LIBS) $(TCTI_TABRMD_LIBS)
+LDADD = $(LIB_COMMON) $(TPM20_TSS_LIBS) $(TCTI_SOCK_LIBS) $(TCTI_DEV_LIBS) $(TCTI_TABRMD_LIBS) $(CRYPTO_LIBS)
 
 sbin_PROGRAMS = \
     tools/tpm2_create \

programming_language: Shell
filename: configure.ac
change_type: ModificationType.MODIFY
diff: @@ -69,7 +69,8 @@ AS_IF(
     [AC_MSG_ERROR(
         [no TCTIs: at least one TCTI library must be enabled],
         [1])])
-PKG_CHECK_MODULES([CURL],[libcurl libcrypto])
+PKG_CHECK_MODULES([CRYPTO],[libcrypto])
+PKG_CHECK_MODULES([CURL],[libcurl])
 AC_ARG_ENABLE([unit],
             [AS_HELP_STRING([--enable-unit],
                             [build cmocka unit tests (default is no)])],

programming_language: Python
filename: tpm_kdfa.c
change_type: ModificationType.MODIFY
diff: @@ -27,20 +27,40 @@
 
 #include <sapi/tpm20.h>
 
+ #include <openssl/err.h>
+#include <openssl/hmac.h>
+
 #include "string-bytes.h"
 #include "tpm_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(TSS2_SYS_CONTEXT *sapi_context, TPMI_ALG_HASH hashAlg,
+TPM_RC tpm_kdfa(TPMI_ALG_HASH hashAlg,
         TPM2B *key, char *label, TPM2B *contextU, TPM2B *contextV, UINT16 bits,
         TPM2B_MAX_BUFFER  *resultKey )
 {
-    TPM2B_DIGEST tmpResult;
     TPM2B_DIGEST tpm2bLabel, tpm2bBits, tpm2b_i_2;
     UINT8 *tpm2bBitsPtr = &tpm2bBits.t.buffer[0];
     UINT8 *tpm2b_i_2Ptr = &tpm2b_i_2.t.buffer[0];
     TPM2B_DIGEST *bufferList[8];
     UINT32 bitsSwizzled, i_Swizzled;
-    TPM_RC rval;
+    TPM_RC rval = TPM_RC_SUCCESS;
     int i, j;
     UINT16 bytes = bits / 8;
 
@@ -64,8 +84,24 @@ TPM_RC tpm_kdfa(TSS2_SYS_CONTEXT *sapi_context, TPMI_ALG_HASH hashAlg,
 
     i = 1;
 
+    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.
     while( resultKey->t.size < bytes )
     {
+        TPM2B_DIGEST tmpResult;
         // Inner loop
 
         i_Swizzled = string_bytes_endian_convert_32( i );
@@ -77,21 +113,41 @@ TPM_RC tpm_kdfa(TSS2_SYS_CONTEXT *sapi_context, TPMI_ALG_HASH hashAlg,
         bufferList[j++] = (TPM2B_DIGEST *)contextU;
         bufferList[j++] = (TPM2B_DIGEST *)contextV;
         bufferList[j++] = (TPM2B_DIGEST *)&(tpm2bBits.b);
-        bufferList[j++] = (TPM2B_DIGEST *)0;
-        rval = tpm_hmac(sapi_context, hashAlg, key, (TPM2B **)&( bufferList[0] ), &tmpResult );
-        if( rval != TPM_RC_SUCCESS )
-        {
-            return( rval );
+        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;
+
         bool res = string_bytes_concat_buffer(resultKey, &(tmpResult.b));
         if (!res) {
-            return TSS2_SYS_RC_BAD_VALUE;
+            rval = TSS2_SYS_RC_BAD_VALUE;
+            goto err;
         }
     }
 
     // Truncate the result to the desired size.
     resultKey->t.size = bytes;
 
-    return TPM_RC_SUCCESS;
+err:
+    HMAC_CTX_cleanup(&ctx);
+
+    return rval;
 }

programming_language: C++
filename: tpm_kdfa.h
change_type: ModificationType.MODIFY
diff: @@ -42,7 +42,7 @@
  * @param resultKey
  * @return
  */
-TPM_RC tpm_kdfa(TSS2_SYS_CONTEXT *sapi_context, TPMI_ALG_HASH hashAlg,
+TPM_RC tpm_kdfa(TPMI_ALG_HASH hashAlg,
         TPM2B *key, char *label, TPM2B *contextU, TPM2B *contextV,
         UINT16 bits, TPM2B_MAX_BUFFER *resultKey );
 

programming_language: C
filename: tpm_session.c
change_type: ModificationType.MODIFY
diff: @@ -198,7 +198,7 @@ static TPM_RC StartAuthSession(TSS2_SYS_CONTEXT *sapi_context, SESSION *session
             }
             else
             {
-                rval = tpm_kdfa(sapi_context, session->authHash, &(key.b), label, &( session->nonceNewer.b ),
+                rval = tpm_kdfa(session->authHash, &(key.b), label, &( session->nonceNewer.b ),
                         &( session->nonceOlder.b ), bytes * 8, (TPM2B_MAX_BUFFER *)&( session->sessionKey ) );
             }
 

programming_language: C