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
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 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).
Possible misuse of DHCP
Do not use the
xid as proof of identity.
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:
Do you still have questions? Questions regarding this advisory should go to email@example.com. To report a new issue, please encrypt your message using firstname.lastname@example.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.
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