krb5 - checksum verification weakness

A vulnerability has been found in krb5, the MIT implementation of
Kerberos.

MIT krb5 clients incorrectly accept unkeyed checksums in the SAM-2
preauthentication challenge: an unauthenticated remote attacker could
alter a SAM-2 challenge, affecting the prompt text seen by the user or
the kind of response sent to the KDC. Under some circumstances, this
can negate the incremental security benefit of using a single-use
authentication mechanism token.

MIT krb5 incorrectly accepts RFC 3961 key-derivation checksums using
RC4 keys when verifying KRB-SAFE messages: an unauthenticated remote
attacker has a 1/256 chance of forging KRB-SAFE messages in an
application protocol if the targeted pre-existing session uses an RC4
session key. Few application protocols use KRB-SAFE messages.

The Common Vulnerabilities and Exposures project has assigned
CVE-2010-1323 to these issues.

For the stable distribution (lenny), these problems have been fixed in
version 1.6.dfsg.4~beta1-5lenny6.

The builds for the mips architecture are not included in this advisory.
They will be released as soon as they are available.

For the testing distribution (squeeze) and the unstable distribution
(sid), these problem have been fixed in version 1.8.3+dfsg-3.

We recommend that you upgrade your krb5 packages.