krb5 - several vulnerabilities

Several vulnerabilities have been discovered in krb5, an
implementation of MIT Kerberos.

• A cryptographic weakness in version 4 of the Kerberos protocol
  allows an attacker to use a chosen-plaintext attack to impersonate
  any principal in a realm. Additional cryptographic weaknesses in
  the krb4 implementation included in the MIT krb5 distribution
  permit the use of cut-and-paste attacks to fabricate krb4 tickets
  for unauthorized client principals if triple-DES keys are used to
  key krb4 services. These attacks can subvert a site’s entire
  Kerberos authentication infrastructure.

Kerberos version 5 does not contain this cryptographic
vulnerability. Sites are not vulnerable if they have Kerberos v4
completely disabled, including the disabling of any krb5 to krb4
translation services.

• The MIT Kerberos 5 implementation includes an RPC library derived
  from SUNRPC. The implementation contains length checks, that are
  vulnerable to an integer overflow, which may be exploitable to
  create denials of service or to gain unauthorized access to
  sensitive information.
• Buffer overrun and underrun problems exist in Kerberos principal
  name handling in unusual cases, such as names with zero components,
  names with one empty component, or host-based service principal
  names with no host name component.

This version of the krb5 package changes the default behavior and
disallows cross-realm authentication for Kerberos version 4. Because
of the fundamental nature of the problem, cross-realm authentication
in Kerberos version 4 cannot be made secure and sites should avoid its
use. A new option (-X) is provided to the krb5kdc and krb524d
commands to re-enable version 4 cross-realm authentication for those
sites that must use this functionality but desire the other security
fixes.

For the stable distribution (woody) this problem has been
fixed in version 1.2.4-5woody4.

The old stable distribution (potato) does not contain krb5 packages.

For the unstable distribution (sid) this problem will be fixed soon.

We recommend that you upgrade your krb5 package.