CVE-2016-2125

Impact:
Moderate
Public Date:
2016-12-19
CWE:
CWE-287
Bugzilla:
1403114: CVE-2016-2125 samba: Unconditional privilege delegation to Kerberos servers in trusted realms
It was found that Samba always requested forwardable tickets when using Kerberos authentication. A service to which Samba authenticated using Kerberos could subsequently use the ticket to impersonate Samba to other services or domain users.

Find out more about CVE-2016-2125 from the MITRE CVE dictionary dictionary and NIST NVD.

CVSS v2 metrics

Base Score 4.3
Base Metrics AV:A/AC:M/Au:N/C:P/I:P/A:N
Access Vector Adjacent Network
Access Complexity Medium
Authentication None
Confidentiality Impact Partial
Integrity Impact Partial
Availability Impact None

CVSS v3 metrics

CVSS3 Base Score 6.4
CVSS3 Base Metrics CVSS:3.0/AV:A/AC:H/PR:N/UI:R/S:U/C:H/I:H/A:N
Attack Vector Adjacent Network
Attack Complexity High
Privileges Required None
User Interaction Required
Scope Unchanged
Confidentiality High
Integrity Impact High
Availability Impact None

Find out more about Red Hat support for the Common Vulnerability Scoring System (CVSS).

Red Hat Security Errata

Platform Errata Release Date
Red Hat Enterprise Linux 6 (samba) RHSA-2017:0662 2017-03-21
Red Hat Gluster 3.2 Samba on RHEL-6 (samba) RHSA-2017:0494 2017-03-23
Red Hat Enterprise Linux 7 (samba) RHSA-2017:1265 2017-05-22
Red Hat Gluster 3.2 Samba on RHEL-7 (samba) RHSA-2017:0495 2017-03-23
Red Hat Enterprise Linux 6 (samba4) RHSA-2017:0744 2017-03-21

Affected Packages State

Platform Package State
Red Hat Gluster Storage 3.1 samba Will not fix
Red Hat Enterprise Linux 5 samba Will not fix
Red Hat Enterprise Linux 5 samba3x Will not fix

Mitigation

The following mitigation is suggested by upstream.

The samba-tool command and the AD DC mode honours the undocumented "gensec_gssapi:delegation=no" option in the [global] section of the smb.conf file.

Controlling Kerberos forwarding
===============================

In the Active Directory world it's possible for administrators to
limit the delegation. User and computer objects can both act as
Kerberos users and also as Kerberos services. Both types of objects have an
attribute called 'userAccountControl' which is a bitmask that controls the
behavior of the account. The following three values have impact on possible
delegation:

0x00100000: UF_NOT_DELEGATED:

The UF_NOT_DELEGATED can be used to disable the ability to get forwardable TGT
for the account. It means the KDC will respond with an error if the client asks
for the forwardable ticket. The client typically gives up and removes the
GSS_C_DELEG_FLAG flag and continues without passing delegated credentials.
Administrators can use this to disable possible delegation for the most
privileged accounts (e.g. administrator accounts).

0x00080000: UF_TRUSTED_FOR_DELEGATION

If the UF_TRUSTED_FOR_DELEGATION is set on an account a KDC will include the
OK_AS_DELEGATE flag in a granted service ticket. If the client application
uses just GSS_C_DELEG_POLICY_FLAG (instead of GSS_C_DELEG_FLAG) gssapi/Kerberos
libraries typically only include delegated credentials when the service ticket
includes the OK_AS_DELEGATE flag. Administrators can use this to control which
services will get delegated credentials, for example if the service runs in a
trusted environment and actually requires the presence of delegated
credentials.

0x01000000: UF_TRUSTED_TO_AUTHENTICATE_FOR_DELEGATION

The UF_TRUSTED_TO_AUTHENTICATE_FOR_DELEGATION is not really relevant for this
CVE and just listed here for completeness. This flag is relevant for the
S4U2Proxy feature, where a service can ask the KDC for a proxied service
ticket which can impersonate users to other services.

External References

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