Vulnerabilities in MIT Kerberos 5

• 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.

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.

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)

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.

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 – http://www.kb.cert.org/vuls/id/795632
• Vulnerability Note VU#866472 – http://www.kb.cert.org/vuls/id/866472
• Vulnerability Note VU#350792 – http://www.kb.cert.org/vuls/id/350792
• Vulnerability Note VU#550464 – http://www.kb.cert.org/vuls/id/550464
• MIT krb5 Security Advisory 2004-002 – http://web.mit.edu/kerberos/advisories/MITKRB5-SA-2004-002-dblfree.txt
• MIT krb5 Security Advisory 2004-003 – http://web.mit.edu/kerberos/www/advisories/MITKRB5-SA-2004-003-asn1.txt
• Kerberos: The Network Authentication Protocol – http://web.mit.edu/kerberos/www/

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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.

Revision History

• September 3, 2004: Initial release

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