MITKRB5-SA-2006-003: kadmind (via GSS-API lib) frees uninitialized pointers

[Tom Yu <tlyu@xxxxxxx>]

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                 MIT krb5 Security Advisory 2006-003

Original release: 2007-01-09
Last update: 2007-01-09

Topic: kadmind (via GSS-API mechglue) frees uninitialized pointers

Severity: CRITICAL

CVE: CVE-2006-6144
CERT: VU#831452

SUMMARY
=======

The Kerberos administration daemon, "kadmind", can free uninitialized
pointers, possibly leading to arbitrary code execution.  This
vulnerability results from memory management bugs in the "mechglue"
abstraction interface of the GSS-API implementation.  Third-party
applications written using the GSS-API may also be vulnerable.

Exploitation of this vulnerability is believed to be difficult.  No
exploit code is known to exist at this time.

IMPACT
======

An unauthenticated user may cause execution of arbitrary code in
kadmind, which can compromise the Kerberos key database and host
security.  (kadmind usually runs as root.)  Unsuccessful exploitation,
or even accidental replication of the required conditions by
non-malicious users, can result in kadmind crashing.

An unauthenticated user may cause execution of arbitrary code in
third-party applications which use the GSS-API library.

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

* kadmind from MIT releases krb5-1.5 through krb5-1.5.1

* third-party applications calling the GSS-API library included in MIT
  releases krb5-1.5 through krb5-1.5.1

* Earlier releases may not be affected because the relevant code was
  not compiled.

FIXES
=====

* The upcoming krb5-1.6 release will contain a fix for this problem.
  Additionally, the upcoming krb5-1.5.2 patch release will contain
  this fix.

* Apply the patch at:

  http://web.mit.edu/kerberos/advisories/2006-003-patch.txt

  A PGP-signed version of the patch is at:

  http://web.mit.edu/kerberos/advisories/2006-003-patch.txt.asc

REFERENCES
==========

This announcement is posted at:

  http://web.mit.edu/kerberos/advisories/MITKRB5-SA-2006-003-mechglue.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

CVE: CVE-2006-6144
http://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2006-6144

CERT: VU#831452
http://www.kb.cert.org/vuls/id/831452

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

This vulnerability was found while investigating a related
vulnerability reported by Andrew Korty of Indiana University.

DETAILS
=======

The specifications for the GSS-API C bindings, including RFC 2744,
require that all GSS-API calls which may return pointers to allocated
memory to initialize the pointers, even in error conditions.  The
implementation of the "mechglue" abstraction interface can execute
error-handling paths which do not complete initialization of output
parameters.  As a result, callers which do not initialize return
structures such as gss_buffer_desc may call destructor functions such
as gss_release_buffer on values containing uninitialized pointers.

In kadmind, the log_badverf() function calls gss_display_name()
without checking its return value and without initializing the
gss_buffer_desc structures passed to gss_display_name().  If
gss_display_name() encounters certain error conditions, it does not
initialize the gss_buffer_t output argument passed to it.  The
log_badverf() function then logs the returned strings, and calls
gss_release_buffer() on these gss_buffer_desc structures.  When
RPCSEC_GSS is used, kadmind uses a NULL server name, so at least one
of the calls to gss_display_name() will always fail in that case.

The act of logging these strings will typically cause a memory access
fault if the uninitialized pointers have values pointing into invalid
address space, which may prevent harmful effects in
gss_release_buffer() because the program will have crashed.  It is
inadvisable to depend on this possibility, because an attacker may be
able to manipulate the uninitialized pointers to take on values
pointing into valid address space.

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

2007-01-09      original release

Copyright (C) 2006 Massachusetts Institute of Technology
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