MITKRB5-SA-2009-003 [CVE-2009-3295] KDC denial of service in cross-realm referral processing

[Tom Yu]

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MITKRB5-SA-2009-003

MIT krb5 Security Advisory 2009-003
Original release: 2009-12-28
Last update: 2009-12-28

Topic: KDC denial of service in cross-realm referral processing

CVE-2009-3295
KDC denial of service in cross-realm referral processing

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

CVSSv2 Base Score:      7.8

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

CVSSv2 Temporal Score:  6.1

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

SUMMARY
=======

A null pointer dereference can occur in an error condition in the KDC
cross-realm referral processing code in MIT krb5-1.7.  This can cause
the KDC to crash.

This is an implementation vulnerability in MIT krb5, and is not a
vulnerability in the Kerberos protocol.

IMPACT
======

An unauthenticated remote attacker could cause the KDC to crash due to
a null pointer dereference.  Legitimate requests can also cause this
crash to occur.

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

* MIT krb5 release krb5-1.7.  Earlier releases did not contain the
  functionality implemented by the vulnerable code.

FIXES
=====

* Upgrade: The upcoming krb5-1.7.1 release will contain a fix for this
  vulnerability.

* Workaround: Disable the realm referral capability by using the
  "no_host_referral = *" setting, e.g.

        [kdcdefaults]
                no_host_referral = *

  or

        [realms]
                EXAMPLE.COM = {
                        # ... other configuration settings ...
                        no_host_referral = *
                }

* Apply the patch:

diff --git a/src/kdc/do_tgs_req.c b/src/kdc/do_tgs_req.c
index 298e132..12180ff 100644
- --- a/src/kdc/do_tgs_req.c
+++ b/src/kdc/do_tgs_req.c
@@ -1158,7 +1158,7 @@ prep_reprocess_req(krb5_kdc_req *request, krb5_principal *krbtgt_princ)
             free(temp_buf);
             if (retval) {
                 /* no match found */
- -                kdc_err(kdc_context, retval, 0);
+                kdc_err(kdc_context, retval, "unable to find realm of host");
                 goto cleanup;
             }
             if (realms == 0) {
diff --git a/src/lib/kadm5/logger.c b/src/lib/kadm5/logger.c
index efff818..ef3735a 100644
- --- a/src/lib/kadm5/logger.c
+++ b/src/lib/kadm5/logger.c
@@ -188,6 +188,9 @@ klog_com_err_proc(const char *whoami, long int code, const char *format, va_list
     char	*cp;
     char	*syslogp;
 
+    if (whoami == NULL || format == NULL)
+        return;
+
     /* Make the header */
     snprintf(outbuf, sizeof(outbuf), "%s: ", whoami);
     /*

  This patch is also available at

  http://web.mit.edu/kerberos/advisories/2009-003-patch.txt

  A PGP-signed patch is available at

  http://web.mit.edu/kerberos/advisories/2009-003-patch.txt.asc

REFERENCES
==========

This announcement is posted at:

  http://web.mit.edu/kerberos/advisories/MITKRB5-SA-2009-003.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-2009-3295
http://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2009-3295

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

This issue was independently discovered by Jeff Blaine, Radoslav Bodo,
Jakob Haufe, and Jorgen Wahlsten.

CONTACT
=======

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

pub   2048R/D9058C24 2009-01-26 [expires: 2010-02-01]
uid     MIT Kerberos Team Security Contact <krbcore-security at mit.edu>

DETAILS
=======

A null pointer dereference exists in new functionality added in
krb5-1.7.  This new functionality produces cross-realm referrals when
a client requests a ticket for a host-based service principal name.
Under certain error conditions, the function prep_reprocess_req() in
do_tgs_req.c calls the kdc_err() function with a null pointer as the
format string, which other code proceeds to dereference, causing a
crash on most platforms.

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

2009-12-28	original release

Copyright (C) 2009 Massachusetts Institute of Technology
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