Jeffrey Altman, Viktor Dukhovni, and Nicolas Williams reported that Heimdal, an implementation of Kerberos 5 that aims to be compatible with MIT Kerberos, trusts metadata taken from the unauthenticated plaintext (Ticket), rather than the authenticated and encrypted KDC response. A man-in-the-middle attacker can use this flaw to impersonate services to the client.
See <https://orpheus-lyre.info/> for details.
For the oldstable distribution (jessie), this problem has been fixed in version 1.6~rc2+dfsg-9+deb8u1.
For the stable distribution (stretch), this problem has been fixed in version 7.1.0+dfsg-13+deb9u1.
For the unstable distribution (sid), this problem has been fixed in version 7.4.0.dfsg.1-1.
We recommend that you upgrade your heimdal packages.