krb5: krb5 may accept authdata checksums with low-entropy derived keys (MITKRB5-SA-2010-007)

MIT Kerberos 5 aka krb5 1.8.x through 1.8.3 does not reject RC4 key-derivation checksums, which might allow remote authenticated users to forge a 1 AD-SIGNEDPATH or 2 AD-KDC-ISSUED signature, and possibly gain privileges, by leveraging the small key space that results from certain one-byte...