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MITKRB5-SA-2011-003

MIT krb5 Security Advisory 2011-003
Original release: 2011-03-15
Last update: 2011-03-15

Topic: KDC vulnerable to double-free when PKINIT enabled

CVE-2011-0284

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

SUMMARY
=======

The MIT Kerberos 5 Key Distribution Center (KDC) daemon is vulnerable
to a double-free condition if the Public Key Cryptography for Initial
Authentication (PKINIT) capability is enabled, resulting in daemon
crash or arbitrary code execution (which is believed to be difficult).

IMPACT
======

An unauthenticated remote attacker can induce a double-free event,
causing the KDC daemon to crash (denial of service), or to execute
arbitrary code.  Exploiting a double-free event to execute arbitrary
code is believed to be difficult.

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

The KDC in releases krb5-1.7 and later are vulnerable, if they are
configured to respond to PKINIT requests.  Earlier releases did not
contain the vulnerable code.  Additionally, third-party
preauthentication plugins that generate TYPED-DATA in the e-data field
of a KRB-ERROR message may be vulnerable.

FIXES
=====

* Upcoming releases in the krb5-1.7, krb5-1.8, and krb5-1.9 series
  will contain fixes.

* Apply the following patch:

diff --git a/src/kdc/do_as_req.c b/src/kdc/do_as_req.c
index 46b5fa1..464cb6e 100644
- --- a/src/kdc/do_as_req.c
+++ b/src/kdc/do_as_req.c
@@ -741,6 +741,8 @@ prepare_error_as (struct kdc_request_state *rstate, krb5_kdc_req *request,
                     pad->contents = td[size]->data;
                     pad->length = td[size]->length;
                     pa[size] = pad;
+                    td[size]->data = NULL;
+                    td[size]->length = 0;
                 }
             krb5_free_typed_data(kdc_context, td);
         }

  This patch is also available at

  http://web.mit.edu/kerberos/advisories/2011-003-patch.txt

  A PGP-signed patch is available at

  http://web.mit.edu/kerberos/advisories/2011-003-patch.txt.asc

REFERENCES
==========

This announcement is posted at:

  http://web.mit.edu/kerberos/advisories/MITKRB5-SA-2011-003.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-2011-0284
http://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2011-0284

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

This issue was discovered by Cameron Meadors of Red Hat.

CONTACT
=======

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

pub   2048R/56CD8F76 2010-12-29 [expires: 2012-02-01]
uid     MIT Kerberos Team Security Contact <krbcore-security@mit.edu>

DETAILS
=======

In do_as_req.c, the function perpare_error_as() attempts to decode the
e_data field both as preauth data and as typed data.  If the e_data
contents are typed data, they are converted to preauth data.  This
conversion can free pointers to the typed data items, and free them
again when cleaning up the preauth data during function exit.

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

2011-03-15      original release

Copyright (C) 2011 Massachusetts Institute of Technology
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