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MITKRB5-SA-2012-001: KDC heap corruption and crash [CVE-2012-1014 CVE-2012-1015]



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MITKRB5-SA-2012-001

MIT krb5 Security Advisory 2012-001
Original release: 2012-07-31

Topic: KDC heap corruption and crash vulnerabilities

CVE-2012-1015: KDC frees uninitialized pointer

CVSSv2 Vector: AV:N/AC:M/Au:N/C:C/I:C/A:C/E:POC/RL:OF/RC:C

CVSSv2 Base Score:      9.3

Access Vector:          Network
Access Complexity:      Medium
Authentication:         None
Confidentiality Impact: Complete
Integrity Impact:       Complete
Availability Impact:    Complete

CVSSv2 Temporal Score:  7.3

Exploitability:         Proof-of-Concept
Remediation Level:      Official Fix
Report Confidence:      Confirmed

CVE-2012-1014: KDC dereferences uninitialized pointer

CVSSv2 Vector: AV:N/AC:L/Au:N/C:P/I:P/A:C/E:POC/RL:OF/RC:C
CVSSv2 Base Score:      9
CVSSv2 Temporal Score:  7

SUMMARY
=======

CVE-2012-1015: The MIT krb5 KDC (Key Distribution Center) daemon can
free an uninitialized pointer while processing an unusual AS-REQ,
corrupting the process heap and possibly causing the daemon to
abnormally terminate.  An attacker could use this vulnerability to
execute malicious code, but exploiting frees of uninitialized pointers
to execute code is believed to be difficult.  It is possible that a
legitimate client that is misconfigured in an unusual way could
trigger this vulnerability.

CVE-2012-1014: The MIT krb5 KDC daemon can dereference an
uninitialized pointer while processing a malformed AS-REQ, causing the
daemon to abnormally terminate.  This vulnerability could
theoretically lead to the execution of malicious code, but that is
believed to be very difficult.

No known exploit exists that is capable of executing malicious code
for either vulnerability, but it is also not difficult to trigger a
denial of service with either vulnerability.

IMPACT
======

CVE-2012-1015: By sending a specially crafted AS-REQ, an
unauthenticated remote attacker can cause the KDC to abnormally
terminate or to execute malicious code.

CVE-2012-1014: By sending a malformed AS-REQ, an unauthenticated
remote attacker can cause the KDC to abnormally terminate.  It is
theoretically possible, but unlikely, for this vulnerability to lead
to the execution of malicious code.

AFFECTED SOFTWARE
=================

* The KDC in releases krb5-1.8 and later is vulnerable to
  CVE-2012-1015.

* The KDC in releases krb5-1.10 and later is vulnerable to
  CVE-2012-1014.

* Some platforms detect attempts to free invalid pointers and
  protectively terminate the process, preventing arbitrary code
  execution on those platforms.

FIXES
=====

* The upcoming krb5-1.10.3 release will contain a fix for
  CVE-2012-1014 and CVE-2012-1015.

* The upcoming krb5-1.9.5 release will contain a fix for
  CVE-2012-1015.

* Apply the following patch:

diff --git a/src/kdc/do_as_req.c b/src/kdc/do_as_req.c
index 23623fe..8ada9d0 100644
- --- a/src/kdc/do_as_req.c
+++ b/src/kdc/do_as_req.c
@@ -463,7 +463,7 @@ process_as_req(krb5_kdc_req *request, krb5_data *req_pkt,
     krb5_enctype useenctype;
     struct as_req_state *state;
 
- -    state = malloc(sizeof(*state));
+    state = calloc(sizeof(*state), 1);
     if (!state) {
         (*respond)(arg, ENOMEM, NULL);
         return;
@@ -486,6 +486,7 @@ process_as_req(krb5_kdc_req *request, krb5_data *req_pkt,
     state->authtime = 0;
     state->c_flags = 0;
     state->req_pkt = req_pkt;
+    state->inner_body = NULL;
     state->rstate = NULL;
     state->sname = 0;
     state->cname = 0;
diff --git a/src/kdc/kdc_preauth.c b/src/kdc/kdc_preauth.c
index 9d8cb34..d4ece3f 100644
- --- a/src/kdc/kdc_preauth.c
+++ b/src/kdc/kdc_preauth.c
@@ -1438,7 +1438,8 @@ etype_info_helper(krb5_context context, krb5_kdc_req *request,
                 continue;
 
             }
- -            if (request_contains_enctype(context, request, db_etype)) {
+            if (krb5_is_permitted_enctype(context, db_etype) &&
+                request_contains_enctype(context, request, db_etype)) {
                 retval = _make_etype_info_entry(context, client->princ,
                                                 client_key, db_etype,
                                                 &entry[i], etype_info2);
diff --git a/src/kdc/kdc_util.c b/src/kdc/kdc_util.c
index a43b291..94dad3a 100644
- --- a/src/kdc/kdc_util.c
+++ b/src/kdc/kdc_util.c
@@ -2461,6 +2461,7 @@ kdc_handle_protected_negotiation(krb5_data *req_pkt, krb5_kdc_req *request,
         return 0;
     pa.magic = KV5M_PA_DATA;
     pa.pa_type = KRB5_ENCPADATA_REQ_ENC_PA_REP;
+    memset(&checksum, 0, sizeof(checksum));
     retval = krb5_c_make_checksum(kdc_context,0, reply_key,
                                   KRB5_KEYUSAGE_AS_REQ, req_pkt, &checksum);
     if (retval != 0)
diff --git a/src/lib/kdb/kdb_default.c b/src/lib/kdb/kdb_default.c
index c4bf92e..367c894 100644
- --- a/src/lib/kdb/kdb_default.c
+++ b/src/lib/kdb/kdb_default.c
@@ -61,6 +61,9 @@ krb5_dbe_def_search_enctype(kcontext, dbentp, start, ktype, stype, kvno, kdatap)
     krb5_boolean        saw_non_permitted = FALSE;
 
     ret = 0;
+    if (ktype != -1 && !krb5_is_permitted_enctype(kcontext, ktype))
+        return KRB5_KDB_NO_PERMITTED_KEY;
+
     if (kvno == -1 && stype == -1 && ktype == -1)
         kvno = 0;
 


  This patch is also available at

  http://web.mit.edu/kerberos/advisories/2012-001-patch.txt

  A PGP-signed patch is available at

  http://web.mit.edu/kerberos/advisories/2012-001-patch.txt.asc

REFERENCES
==========

This announcement is posted at:

  http://web.mit.edu/kerberos/advisories/MITKRB5-SA-2012-001.txt

This announcement and related security advisories may be found on the
MIT Kerberos security advisory page at:

        http://web.mit.edu/kerberos/advisories/index.html

The main MIT Kerberos web page is at:

        http://web.mit.edu/kerberos/index.html

CVSSv2:

    http://www.first.org/cvss/cvss-guide.html
    http://nvd.nist.gov/cvss.cfm?calculator&adv&version=2

CVE: CVE-2012-1014
http://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2012-1014

CVE: CVE-2012-1015
http://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2012-1015

ACKNOWLEDGMENTS
===============

We thank Emmanuel Bouillon (NCI Agency) for discovering and reporting
these vulnerabilities.

CONTACT
=======

The MIT Kerberos Team security contact address is
<krbcore-security@xxxxxxx>.  When sending sensitive information,
please PGP-encrypt it using the following key:

pub   2048R/07566CE5 2012-01-27 [expires: 2013-02-01]
uid     MIT Kerberos Team Security Contact <krbcore-security@xxxxxxx>

DETAILS
=======

CVE-2012-1015: KDC frees uninitialized pointer

The KDC function kdc_handle_protected_negotiation(), which handles the
protected negotiation feature of the FAST Kerberos protocol extension,
can attempt to create a checksum using a key type that is invalid for
producing checksums.  This causes its call to krb5_c_make_checksum()
to fail, which leads to the cleanup code in
kdc_handle_protected_negotiation() freeing an uninitialized pointer.

It is possible, but unlikely, for a legitimate client to be
misconfigured in a way that causes the KDC to attempt to use such an
invalid key type in this code.

CVE-2012-1014: KDC dereferences uninitialized pointer

CVSSv2 Vector: AV:N/AC:L/Au:N/C:P/I:P/A:C/E:POC/RL:OF/RC:C

CVSSv2 Base Score:      9

Access Vector:          Network
Access Complexity:      Low
Authentication:         None
Confidentiality Impact: Partial
Integrity Impact:       Partial
Availability Impact:    Complete

CVSSv2 Temporal Score:  7

Exploitability:         Proof-of-Concept
Remediation Level:      Official Fix
Report Confidence:      Confirmed

The KDC function process_as_req(), which handles incoming AS-REQ
messages, allocates a state object using malloc() and initializes many
fields within it.  It fails to initialize state->inner_body, which is
a pointer to a krb5_data object.  If the uninitialized value
state->inner_body is not null, a failure in process_as_req() that
precedes the call to kdc_find_fast() could cause error handling code
in finish_process_as_req() to pass the uninitialized state->inner_body
pointer to krb5_free_data(), which would proceed to dereference the
uninitialized pointer.  The typical outcome is KDC process termination
due to a segmentation fault or similar memory fault.

It is theoretically possible for an attacker to manipulate the
contents of the heap so that the uninitialized pointer
state->inner_body would point to valid memory where
state->inner_body->data contains an attacker-chosen invalid pointer
value.  The krb5_free_data() function would then pass this invalid
pointer to free().  This could allow the attacker to overwrite memory
or execute malicious code on some platforms, depending on the details
of the malloc() implementation.  This indirect attack method seems
much less likely to succeed than one where the attacker could directly
control the invalid pointer value that the program passes to free().

REVISION HISTORY
================

2012-07-31      original release

Copyright (C) 2012 Massachusetts Institute of Technology
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