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MITKRB5-SA-2011-001

MIT krb5 Security Advisory 2011-001
Original release: 2011-02-08
Last update: 2011-02-08

Topic: kpropd denial of service

CVE-2010-4022

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

CVSSv2 Base Score:      5

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

CVSSv2 Temporal Score:  4.4

Exploitability:         High
Remediation Level:      Official Fix
Report Confidence:      Confirmed

SUMMARY
=======

The MIT krb5 KDC database propagation daemon (kpropd) is vulnerable to
a denial-of-service attack triggered by invalid network input.  If a
kpropd worker process receives invalid input that causes it to exit
with an abnormal status, it can cause the termination of the listening
process that spawned it, preventing the slave KDC it was running on
from receiving database updates from the master KDC.

Exploit code is not known to exist, but the vulnerability is easy to
trigger manually.

IMPACT
======

An unauthenticated remote attacker can cause kpropd running in
standalone mode (the "-S" option) to terminate its listening process,
preventing database propagations to the KDC host on which it was
running.  Configurations where kpropd runs in incremental propagation
mode ("iprop") or as an inetd server are not affected.

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

kpropd in releases krb5-1.7 and later are vulnerable.  Earlier
releases did not contain the incremental propagation implementation
that inadvertently introduced this problem.

FIXES
=====

* Workaround: if incremental propagation is not configured, run kpropd
  as an inetd service.

* Future patch releases for 1.7, 1.8, and 1.9 will contain a fix.

* Apply the patch:

diff -up krb5/src/slave/kpropd.c krb5/src/slave/kpropd.c
- --- krb5/src/slave/kpropd.c  2010-12-17 11:14:26.000000000 -0500
+++ krb5/src/slave/kpropd.c  2010-12-17 11:41:19.000000000 -0500
@@ -404,11 +404,11 @@ retry:
             }
 
             close(s);
- -            if (iproprole == IPROP_SLAVE)
+            if (iproprole == IPROP_SLAVE) {
                 close(finet);
- -
- -            if ((ret = WEXITSTATUS(status)) != 0)
- -                return (ret);
+                if ((ret = WEXITSTATUS(status)) != 0)
+                    return (ret);
+            }
         }
         if (iproprole == IPROP_SLAVE)
             break;

  This patch is also available at

  http://web.mit.edu/kerberos/advisories/2011-001-patch.txt

  A PGP-signed patch is available at

  http://web.mit.edu/kerberos/advisories/2011-001-patch.txt.asc

REFERENCES
==========

This announcement is posted at:

  http://web.mit.edu/kerberos/advisories/MITKRB5-SA-2011-001.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:
http://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2010-4022

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

This issue was discovered by Keiichi Mori 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/8B8DF501 2010-01-15 [expires: 2011-02-01]
uid     MIT Kerberos Team Security Contact <krbcore-security@mit.edu>

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

DETAILS
=======

As a result of the changes implementing incremental propagation, the
do_standalone() function in kpropd.c gained a flaw in child process
handling.  The do_iprop() function, which implements the bulk of the
incremental propagation capability, may need to receive a full
database dump from the master KDC, and calls do_standalone() with an
iprop_role argument of IPROP_SLAVE to partially emulate the behavior
of an ordinary (non-incremental) kpropd.  Unlike in earlier versions
of kpropd, do_standalone() returns the child's exit status (and thus
ceases accepting connections) if the worker process child exits
abnormally, rather than ignoring it.  The correct behavior when
receiving an abnormal exit status from the child process would be to
return from do_standalone() only when invoked from do_iprop().

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

2011-02-08      original release

Copyright (C) 2010 Massachusetts Institute of Technology
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