[OpenAFS] OpenAFS Security Releases 1.8.2, 1.6.23 available --> butc & backup security update question

Thu, 13 Sep 2018 14:37:23 -0400

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It is unfortunate that the announcement e-mail included neither a URL to
the https://www.openafs.org/security/ page nor a link to the individual
security advisory text files:

  https://www.openafs.org/pages/security/OPENAFS-SA-2018-001.txt
  https://www.openafs.org/pages/security/OPENAFS-SA-2018-002.txt
  https://www.openafs.org/pages/security/OPENAFS-SA-2018-003.txt

In the case of OPENAFS-SA-2018-001.txt, both 'butc' and 'backup' (or
'afsbackup' as it is installed on some systems) must be at least:

 * AuriStorFS v0.175
 * OpenAFS 1.8.2
 * OpenAFS 1.6.23

The version of the vlserver, buserver and volserver does not matter.
Those services already supported authenticated and potentially encrypted
connections.

The underlying cause of the incompatibility is that the 'butc' service
would only accept unauthenticated (rxnull) connections and therefore the
'backup' command could only create unauthenticated (rxnull) connections
even if the 'backup' command was executed with -localauth.

As of the releases above, the 'butc' service (by default) will not only
accept authenticated connections but will require that the authenticated
identity be a super-user as reported by the butc host's "bos listusers"
command.

There is no incompatibility with vlserver, buserver and volserver
because those services already accepted authenticated connections and
required that authenticated identities be super-users in order to
create, read, modify, or delete sensitive information.

The privilege escalation is due to 'butc' accepting unauthenticated
requests and executing them using a super-user identity when contacting
the vlserver, buserver, and volserver.

I cannot stress enough how important it is for sites that are running
the AFS backup suite to immediately:

 . upgrade all instances of 'butc' and 'backup'.

 . firewall the 'butc' ports from all machines except those from
   which 'backup' is expected to be issued from.  The butc port is
   (7021 + butc port offset)/udp.  The default offset is 0.

Otherwise, an anonymous attacker can read, alter or destroy the content
of any volume in the cell as well as any backups that do not require
manual intervention by a system administrator to gain access to.

AuriStor coordinated the release of these changes with the OpenAFS
Security officer(s) because this privilege escalation is not only
remotely exploitable but compromises the security and integrity of all
data stored within an AFS cell that operates a Backup Tape Controller
(butc) instance.

The AuriStorFS v0.175 release extends the AuriStorFS security model to
backup with the use of AES256-CTS-HMAC-SHA1-96 wire encryption for all
volume data communications and the use of volume security policies to
ensure that volumes cannot be restored to a fileserver with an
incompatible security policy.

Jeffrey Altman
AuriStor, Inc.

On 9/13/2018 3:12 AM, Giovanni Bracco wrote:
> Hello everybody!
>=20
> I have read about the butc & backup security update.
>=20
> We run daily the AFS backup and I would like to understand if I need
> just to update the backup server with the new butc/backup modules or I
> need also to update all our file servers in order to match the new
> security improvements connected to backup.
>=20
> Giovanni
>=20
> On 11/09/2018 21:04, Benjamin Kaduk wrote:
>>
>> OPENAFS-SA-2018-001 only affects deployments that run the 'butc' utili=
ty
>> as part of the in-tree backup system, but is of high severity for
>> those sites which are affected -- an anonymous attacker could replace
>> entire volumes with attacker-controlled contents.
>>
>> The changes to fix OPENAFS-SA-2018-001 require behavior change in both=
       =20
>> butc(8) and backup(8) to use authenticated connections; old and new
>> versions of these utilities will not interoperate absent specific
>> configuration of the new tool to use the old (insecure) behavior.
>> These changes also are expected to cause backup(8)'s interactive mode
>> to be limited to only butc connections requiring (or not requiring)
>> authentication within a given interactive session, based on the initia=
l
>> arguments selected.
>>
>> Bug reports should be filed to openafs-bugs@openafs.org.
>>
>> Benjamin Kaduk
>> for the OpenAFS Guardians
>>
>=20

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fn:Jeffrey Altman
n:Altman;Jeffrey
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email;internet:jaltman@auristor.com
title:Founder and CEO
tel;work:+1-212-769-9018
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