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.