== Subject:     Access controlled AD LDAP attributes can be discovered
== CVE ID#:     CVE-2023-0614
== Versions:    All Samba releases since Samba 4.0

== Summary:     The fix in 4.6.16, 4.7.9, 4.8.4 and 4.9.7 for
                CVE-2018-10919 Confidential attribute disclosure via
                LDAP filters was insufficient and an attacker may be
                able to obtain confidential BitLocker recovery keys
                from a Samba AD DC.

                Installations with such secrets in their Samba AD
                should assume they have been obtained and need


In Active Directory, there are essentially four different classes of

 - Secret attributes (such as a user, computer or domain trust
   password) that are never disclosed and are not available to search
   against over LDAP.  This is a hard-coded list, and since Samba 4.8
   these are additionally encrypted in the DB with a per-DB key.

 - Confidential attributes (marked as such in the schema) that have a
   default access restriction allowing access only to the owner of the

   While a Samba AD Domain makes these attributes available,
   thankfully by default it will not have any of these confidential
   attributes set, as they are only added by clients after
   configuration (typically via a GPO).

   Examples of confidential data stored in Active Directory include
   BitLocker recovery keys, TPM owner passwords, and certificate
   secret keys stored with Credential Roaming.

 - Access controlled attributes (for reads or writes), Samba will
   honour the access control specified in the ntSecurityDescriptor.

 - Public attributes for read.  Most attributes in Active Directory
   are available to read by all authenticated users.

Because the access control rules for a given attribute are not
consistent between objects, Samba implemented access control
restrictions only after matching objects against the filter.

Taking each of the above classes in turn:

 - Secret attributes are prevented from disclosure firstly by
   redaction of the LDAP filter, and secondly by the fact that they
   are still encrypted during filter processing (by default).

 - Confidential and access controlled attributes were subject to an
   attack using LDAP filters.

With this security patch, for attributes mentioned in the search
filter, Samba will perform a per-object access control evaluation
before LDAP filter matching on the attribute, preventing unauthorised
disclosure of the value of (for example) BitLocker recovery keys.

It is not expected that all similar attacks have been prevented, and
it is likely still possible to determine if an object or attribute on
an object is present, but not to obtain the contents.

Further steps

Evidence of an attack will not show up in the logs, except at the
highly verbose level 10, and there is no record as to if a previous
attribute disclosure has taken place.

In addition to updating Samba, it is strongly recommended that steps
be taken to ensure that data that may have been leaked from
confidential or otherwise access-controlled attributes is no longer

Such steps may include, but are not limited to, re-encrypting
BitLocker encrypted drives, changing TPM passwords, and revoking and
re-issuing certificates that are stored by Credential Roaming (with
new secret keys).

Impacted attributes

In addition to any per-object access control restrictions, the
following attributes in the 2012R2 AD schema have
SEARCH_FLAG_CONFIDENTIAL set in the searchFlags by default:



   Group Managed Service Accounts:
    (this AD DC feature is not implemented in Samba, and exists only
    in Windows 2012 and later, but could have been replicated to Samba
    in a mixed domain):


   unixUserPassword (this value is not used or updated by Samba)

The confidential attributes on your server can be seen (adapt for your
local environment) with:
ldbsearch -U$USERNAME -H ldap://$SERVER -b CN=Schema,CN=Configuration,$BASE_DN '(&(objectClass=attributeSchema)(searchFlags:1.2.840.113556.1.4.803:=128))' lDAPDisplayName

However, please again note that while unlikely, it is possible via the
nTSecurityDescriptor for any attribute to be made access controlled on
any object, and these cases will not be shown by this command.

Limitations for indexed attributes

Additionally, due to the nature of our object indexes, Samba must
evaluate these prior to ACL checking, so read access controlled
information should not be stored in indexed attributes.  This will
allow a timing attack.

Again, taking each of the above classes in turn:

 - Secret attributes cannot be indexed or searched for, so have always
   been protected

 - Confidential attributes are further protected, as this patch will
   prevent attributes marked as 'confidential' from being indexed.
   Search results for these will be safer, but slower.  The impacted
   attributes on your server can be seen (adapt for your local
   environment) with:

   ldbsearch -U$USERNAME -H ldap://$SERVER -b CN=Schema,CN=Configuration,$BASE_DN '(&(objectClass=attributeSchema)(searchFlags:1.2.840.113556.1.4.803:=129))' lDAPDisplayName

   (This will normally return no results and no such attributes have
   this combination by default)
 - Access controlled attributes that are also indexed may be subject
   to timing attacks.

   The list of indexed attributes can be seen (adapt for your local
   environment) with:

   ldbsearch -U$USERNAME -H ldap://$SERVER -b CN=Schema,CN=Configuration,$BASE_DN '(&(objectClass=attributeSchema)(searchFlags:1.2.840.113556.1.4.803:=1))' lDAPDisplayName

Performance impact

As candidate objects are ACL checked before being compared with the
LDAP filter, avoiding this disclosure, Samba's AD DC LDAP read
performance is reduced, with a 20% performance cost in the worst cases
from our existing performance tests.

Further optimisation of the Samba AD DC LDAP server to ameliorate this
impact has been investigated and is technically possible, but is out
of scope for this security release.

Patch Availability

Patches addressing both these issues have been posted to:

Additionally, Samba $VERSIONS have been issued
as security releases to correct the defect.  Samba administrators are
advised to upgrade to these releases or apply the patch as soon
as possible.

CVSSv3 calculation

CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:H/I:N/A:N (7.7)


Do not store confidential information in Active Directory, other than
passwords or keys required for AD operation (as these are in the
hard-coded secret attribute list).


Originally reported by Demi Marie Obenour of Invisible Things Lab.

Patches provided by Joseph Sutton of Catalyst and the Samba team,
reviewed by Andrew Bartlett of Catalyst and the Samba Team.

Advisory by Andrew Bartlett of Catalyst and the Samba Team in
collaboration with Joseph Sutton and Demi Marie Obenour.

== Our Code, Our Bugs, Our Responsibility.
== The Samba Team