CVE-2020-25721: Input Validation
As per upstream report:
In order to avoid issues like CVE-2020-25717 AD Kerberos accepting services need access to unique, and ideally long-term stable identifiers of a user to perform authorization.
The AD PAC provides this, but the most useful information is kept in a buffer which is NDR encoded, which means that so far in Free Software only Samba and applications which use Samba components under the hood like FreeIPA and SSSD decode PAC.
Recognising that the issues seen in Samba are not unique, Samba now provides an extension to UPNDNSINFO, a component of the AD PAC, in a way that can be parsed using basic pointer handling.
From this, future non-Samba based Kerberised applications can easily obtain the user's SID, in the same packing as objectSID in LDAP, confident that the ticket represents a specific user, not matter subsequent renames.
This will allow such non-Samba applications to avoid confusing one Kerberos user for another, even if they have the same string name (due to the gap between time of ticket printing by the KDC and time of ticket acceptance).
Other sources
Kerberos acceptors need easy access to stable AD identifiers (eg objectSid). Samba as an AD DC now provides a way for Linux applications to obtain a reliable SID (and samAccountName) in issued tickets.
— Launchpad
Affected Software
Event History
Frequently Asked Questions
What is the vulnerability ID?
The vulnerability ID is CVE-2020-25721.
What is the severity of CVE-2020-25721?
The severity of CVE-2020-25721 is high with a CVSS score of 8.8.
What software versions are affected by CVE-2020-25721?
Samba versions 4.13.0 to 4.13.14, 4.14.0 to 4.14.10, and 4.15.0 to 4.15.2 are affected.
How can Linux applications obtain a reliable SID and samAccountName in issued tickets with Samba?
Samba as an Active Directory Domain Controller provides a way for Linux applications to obtain a reliable SID and samAccountName in issued tickets.
Where can I find more information about CVE-2020-25721?
You can find more information about CVE-2020-25721 in the following references: [Bugzilla Red Hat](https://bugzilla.redhat.com/show_bug.cgi?id=2021728), [Bugzilla Samba](https://bugzilla.samba.org/show_bug.cgi?id=14725), [Gentoo Security](https://security.gentoo.org/glsa/202309-06).