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List:       dhcp-announce
Subject:    Operational Notification for ISC DHCP 4.4.3
From:       Peter Davies <peterd () isc ! org>
Date:       2022-03-09 17:08:20
Message-ID: 2e1a2fdb-ec7b-d12e-9dae-6787039142cd () isc ! org
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To the users of ISC DHCP:

Today we have released ISC dhcp server version 4.4.3.

This release addresses the problem of insufficient randomness, which can
cause the xid to be predictable under certain circumstances, when dhclient
generates the xid field.

The following Operational Notification explains the issue.

Operational Notification for ISC DHCP 4.4.3

Posting date: 9 March 2022

Program impacted: ISC DHCP

Versions affected: ISC DHCP client - all versions prior to 4.4.3

Description:
DHCP messages sent from a client include a transaction ID (xid). This is 
used
to allow DHCP servers to differentiate between requests, per RFC2131, 
Section
4.1.

Prior to release 4.4.3, the ISC DHCP client dhclient used various pieces of
system information, including unixtime, to generate an xid.

Although the xid was never intended to be used for security purposes, some
environments are known to use it in that way. For an example, please see
https://github.com/irsl/gcp-dhcp-takeover-code-exec.

In light of this, the generation of the xid in ISC DHCP release 4.4.3 
has been
altered so that the randomness will be automatically seeded from a 
configurable
source such as /dev/random (default).

Impact:
Possible misuse of DHCP

Workarounds:
Do not use the xid as proof of identity.

Solution:
Since the workaround listed above is not effective against deliberate
exploitation, ISC recommends that operators running an affected release of
dhclient install release 4.4.3.

Downloads are available via the ISC download page:
https://www.isc.org/download#DHCP

and release notes for the updated releases can be viewed at this link:

4.4.3: https://downloads.isc.org/isc/dhcp/4.4.3/dhcp-4.4.3-RELNOTES

This notification may also be found at:
https://kb.isc.org/article/operational-notification-for-isc-dhcp-443

Do you still have questions? Questions regarding this advisory should go to
security-officer@isc.org. To report a new issue, please encrypt your 
message
using security-officer@isc.org's PGP key which can be found here:
https://www.isc.org/pgpkey/. If you are unable to use encrypted email, 
you may
also report new issues at: https://www.isc.org/reportbug/.

Note: ISC patches only currently supported versions. When possible we 
indicate
EOL versions affected. (For current information on which versions are 
actively
supported, please see https://www.isc.org/download/).

ISC Security Vulnerability Disclosure Policy: Details of our current 
security
advisory policy and practice can be found here: ISC Software Defect and
Security Vulnerability Disclosure Policy.

This Knowledgebase article is the complete and official operational
notification document.

Legal Disclaimer:

Internet Systems Consortium (ISC) is providing this notice on an "AS IS" 
basis.
No warranty or guarantee of any kind is expressed in this notice and none
should be implied. ISC expressly excludes and disclaims any warranties
regarding this notice or materials referred to in this notice, including,
without limitation, any implied warranty of merchantability, fitness for a
particular purpose, absence of hidden defects, or of non-infringement. 
Your use
or reliance on this notice or materials referred to in this notice is at 
your
own risk. ISC may change this notice at any time. A stand-alone copy or
paraphrase of the text of this document that omits the document URL is an
uncontrolled copy. Uncontrolled copies may lack important information, 
be out
of date, or contain factual errors.

-- 
Peter Davies ISC Support


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