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                        National Cyber Alert System

                  Technical Cyber Security Alert TA04-247A


Vulnerabilities in MIT Kerberos 5

   Original release date: September 3, 2004
   Last revised: --
   Source: US-CERT


Systems Affected

     * MIT Kerberos 5 versions prior to krb5-1.3.5

     * Applications that use versions of MIT Kerberos 5 libraries prior
       to krb5-1.3.5

     * Applications that contain code derived from MIT Kerberos 5

   Updated vendor information is available in the systems affected
   section of the individual vulnerability notes.


Overview

   The MIT Kerberos 5 implementation contains several vulnerabilities,
   the most severe of which could allow an unauthenticated, remote
   attacker to execute arbitrary code on a Kerberos Distribution Center
   (KDC). This could result in the compromise of an entire Kerberos
   realm.


I. Description

   There are several vulnerabilities in the MIT implementation of the
   Kerberos 5 protocol. With one exception (VU#550464), all of the
   vulnerabilities involve insecure deallocation of heap memory
   (double-free vulnerabilities) during error handling and Abstract
   Syntax Notation One (ASN.1) decoding. For further details, please see
   the following vulnerability notes:

   VU#795632 - MIT Kerberos 5 ASN.1 decoding functions insecurely
   deallocate memory (double-free)

    The MIT Kerberos 5 library does not securely deallocate heap memory
    when decoding ASN.1 structures, resulting in double-free
    vulnerabilities. An unauthenticated, remote attacker could execute
    arbitrary code on a KDC server, which could compromise an entire
    Kerberos realm. An attacker may also be able to execute arbitrary code
    on Kerberos clients, or cause a denial of service on KDCs or clients.
    (Other resources: MITKRB5-SA-2004-002, CAN-2004-0642)

   VU#866472 - MIT Kerberos 5 ASN.1 decoding function krb5_rd_cred()
   insecurely deallocates memory (double-free)

    The krb5_rd_cred() function in the MIT Kerberos 5 library does not
    securely deallocate heap memory when decoding ASN.1 structures,
    resulting in a double-free vulnerability. A remote, authenticated
    attacker could execute arbitrary code or cause a denial of service on
    any system running an application that calls krb5_rd_cred(). This
    includes Kerberos application servers and other applications that
    process Kerberos authentication via the MIT Kerberos 5 library,
    Generic Security Services Application Programming Interface (GSSAPI),
    and other libraries.
    (Other resources: MITKRB5-SA-2004-002, CAN-2004-0643)

   VU#350792 - MIT Kerberos krb524d insecurely deallocates memory
   (double-free)

    The MIT Kerberos krb524d daemon does not securely deallocate heap
    memory when handling an error condition, resulting in a double-free
    vulnerability. An unauthenticated, remote attacker could execute
    arbitrary code on a system running krb524d, which in many cases is
    also a KDC. The compromise of a KDC system can lead to the compromise
    of an entire Kerberos realm. An attacker may also be able to cause a
    denial of service on a system running krb524d.
    (Other resources: MITKRB5-SA-2004-002, CAN-2004-0772)

   VU#550464 - MIT Kerberos 5 ASN.1 decoding function asn1buf_skiptail()
   does not properly terminate loop

    The asn1buf_skiptail() function in the MIT Kerberos 5 library does not
    properly terminate a loop, allowing an unauthenticated, remote
    attacker to cause a denial of service in a KDC, application server, or
    Kerberos client.
    (Other resources: MITKRB5-SA-2004-003, CAN-2004-0644)


II. Impact

   The impacts of these vulnerabilities vary, but an attacker may be able
   to execute arbitrary code on KDCs, systems running krb524d (typically
   also KDCs), application servers, applications that use Kerberos
   libraries directly or via GSSAPI, and Kerberos clients. An attacker
   could also cause a denial of service on any of these systems.

   The most severe vulnerabilities could allow an unauthenticated, remote
   attacker to execute arbitrary code on a KDC system. This could result
   in the compromise of both the KDC and an entire Kerberos realm.


III. Solution

Apply a patch or upgrade

   Check with your vendor(s) for patches or updates. For information
   about a specific vendor, please see the systems affected sections in
   the individual vulnerability notes or contact your vendor directly.

   Alternatively, apply the appropriate source code patch(es) referenced
   in MITKRB5-SA-2004-002 and MITKRB5-SA-2004-003 and recompile.

   These vulnerabilities will be addressed in krb5-1.3.5.


Appendix A. References

     * Vulnerability Note VU#795632 -
       <https://www.kb.cert.org/vuls/id/795632>

     * Vulnerability Note VU#866472 -
       <https://www.kb.cert.org/vuls/id/866472>

     * Vulnerability Note VU#350792 -
       <https://www.kb.cert.org/vuls/id/350792>

     * Vulnerability Note VU#550464 -
       <https://www.kb.cert.org/vuls/id/550464>

     * MIT krb5 Security Advisory 2004-002 -
       <https://web.mit.edu/kerberos/advisories/MITKRB5-SA-2004-002-dblfre
       e.txt>

     * MIT krb5 Security Advisory 2004-003 -
       <https://web.mit.edu/kerberos/www/advisories/MITKRB5-SA-2004-003-as
       n1.txt>

     * Kerberos: The Network Authentication Protocol -
       <https://web.mit.edu/kerberos/www/>

  _______________________________________________________________________

   Thanks to Tom Yu and the MIT Kerberos Development team for addressing
   these vulnerabilities and coordinating with vendors. MIT credits the
   following people: Will Fiveash, Joseph Galbraith, John Hawkinson, Marc
   Horowitz, and Nico Williams.
  _______________________________________________________________________


   Feedback can be directed to the author: Art Manion

  _______________________________________________________________________

   This document is available from:
   
     <https://www.us-cert.gov/cas/techalerts/TA04-245A.html>
  _______________________________________________________________________


   Copyright 2004 Carnegie Mellon University. Terms of use

   Terms of use: <https://www.us-cert.gov/legal.html>

  _______________________________________________________________________

   Revision History

    September 3, 2004: Initial release

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