Bug 1959397 (CVE-2020-13529)

Summary:	CVE-2020-13529 systemd: DHCP FORCERENEW authentication not implemented can cause a system running the DHCP client to have its network reconfigured
Product:	[Other] Security Response	Reporter:	Guilherme de Almeida Suckevicz <gsuckevi>
Component:	vulnerability	Assignee:	Red Hat Product Security <security-response-team>
Status:	CLOSED ERRATA	QA Contact:
Severity:	medium	Docs Contact:
Priority:	medium
Version:	unspecified	CC:	acardace, atragler, bdettelb, bgalvani, fedoraproject, fge, filbranden, flepied, kaycoth, lnykryn, lpoetter, lrintel, msekleta, nm-team, rkhan, sparks, ssahani, s, sukulkar, systemd-maint-list, systemd-maint, till, tomckay, vmugicag, yuwatana, zbyszek, zjedrzej
Target Milestone:	---	Keywords:	Security
Target Release:	---
Hardware:	All
OS:	Linux
Whiteboard:
Fixed In Version:		Doc Type:	If docs needed, set a value
Doc Text:	An exploitable denial of service vulnerability exists in systemd which does not fully implement RFC3203, as it does not support authentication of FORCERENEW packets. A specially crafted DHCP FORCERENEW packet can cause a system, running the DHCP client, to be vulnerable to a DHCP ACK spoofing attack. An attacker can forge a pair of FORCERENEW and DCHPACK packets to reconfigure the system with arbitrary network settings.	Story Points:	---
Clone Of:		Environment:
Last Closed:	2021-11-09 22:21:33 UTC	Type:	---
Regression:	---	Mount Type:	---
Documentation:	---	CRM:
Verified Versions:		Category:	---
oVirt Team:	---	RHEL 7.3 requirements from Atomic Host:
Cloudforms Team:	---	Target Upstream Version:
Embargoed:
Bug Depends On:	1962041, 1959398, 1961234, 1961238, 1961239, 1961240, 1961241, 1961251, 1962040, 1966123
Bug Blocks:	1959399

Description Guilherme de Almeida Suckevicz 2021-05-11 13:09:58 UTC

An exploitable denial-of-service vulnerability exists in Systemd 245. A specially crafted DHCP FORCERENEW packet can cause a server running the DHCP client to be vulnerable to a DHCP ACK spoofing attack. An attacker can forge a pair of FORCERENEW and DCHP ACK packets to reconfigure the server.

References:
https://talosintelligence.com/vulnerability_reports/TALOS-2020-1142
https://github.com/systemd/systemd/issues/16774

Comment 1 Guilherme de Almeida Suckevicz 2021-05-11 13:10:37 UTC

Created systemd tracking bugs for this issue:

Affects: fedora-all [bug 1959398]

Comment 2 Riccardo Schirone 2021-05-17 14:43:15 UTC

DHCP reconfigure extension RFC: https://datatracker.ietf.org/doc/html/rfc3203

Comment 3 Riccardo Schirone 2021-05-17 14:43:57 UTC

Authentication for DHCP Messages RFC: https://datatracker.ietf.org/doc/html/rfc3118

Comment 8 Riccardo Schirone 2021-05-17 16:06:19 UTC

systemd in upstream version v216 introduced partial support for DHCP FORCERENEW (RFC 3203) with [1]. However authentication of FORCERENEW packets is not implemented, thus it is possible for an adjacent attacker on the local network to forge such packets and trick a system into re-accepting DHCPACK packets, which include all the network settings.

[1] https://github.com/systemd/systemd/commit/615c1467c81411bf1d19fd7092e8995b5ebadc13

Comment 9 Riccardo Schirone 2021-05-17 16:08:50 UTC

There is no available fix at this time for this issue, as upstream is considering this issue as a RFE rather than a vulnerability [2].

[2] https://bugzilla.redhat.com/show_bug.cgi?id=1959398#c2

Comment 12 Riccardo Schirone 2021-06-24 09:06:08 UTC

Temporary fix upstream, at least until RFC6704 (Forcerenew Nonce Authentication) is implemented:
https://github.com/systemd/systemd/commit/6222acc2b59309ac6187450d9e65eceb1b7cc1c5

Comment 14 errata-xmlrpc 2021-11-09 18:28:27 UTC

This issue has been addressed in the following products:

  Red Hat Enterprise Linux 8

Via RHSA-2021:4361 https://access.redhat.com/errata/RHSA-2021:4361

Comment 15 Product Security DevOps Team 2021-11-09 22:21:30 UTC

This bug is now closed. Further updates for individual products will be reflected on the CVE page(s):

https://access.redhat.com/security/cve/cve-2020-13529