Bug 1661252 (CVE-2018-1000845)

Summary:	CVE-2018-1000845 avahi: DNS amplification and reflection to spoofed addresses
Product:	[Other] Security Response	Reporter:	Pedro Sampaio <psampaio>
Component:	vulnerability	Assignee:	Red Hat Product Security <security-response-team>
Status:	CLOSED DUPLICATE	QA Contact:
Severity:	medium	Docs Contact:
Priority:	medium
Version:	unspecified	CC:	bmcclain, dblechte, dfediuck, eedri, mgoldboi, michal.skrivanek, nsl, rschiron, sbonazzo, sherold, trent, yturgema
Target Milestone:	---	Keywords:	Security
Target Release:	---
Hardware:	All
OS:	Linux
Whiteboard:
Fixed In Version:		Doc Type:	If docs needed, set a value
Doc Text:		Story Points:	---
Clone Of:		Environment:
Last Closed:	2019-01-31 08:18:03 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:	1661253
Bug Blocks:	1661254

Description Pedro Sampaio 2018-12-20 15:33:24 UTC

Avahi-daemon in Avahi through 0.7 inadvertently sends Legacy Unicast
Responses to IPv4 unicast queries with source addresses that are not
link-local, which allows remote attackers to cause a denial of service
(traffic amplification) or obtain potentially sensitive information
via port-5353 UDP packets.

send(IP(src="1.1.1.1",dst="192.168.1.1")/UDP(sport=53,
dport=5353)/DNS(rd=1,qd=DNSQR(qtype="PTR", qname="_ssh._tcp.local.")))

Upstream issue:

https://github.com/lathiat/avahi/issues/203

Comment 1 Pedro Sampaio 2018-12-20 15:33:36 UTC

Created avahi tracking bugs for this issue:

Affects: fedora-all [bug 1661253]

Comment 2 Nicholas Luedtke 2018-12-20 17:47:38 UTC

This looks to be CVE-2018-1000845.

Comment 3 Trent Lloyd 2018-12-22 01:29:49 UTC

I have pushed a fix upstream for the issue here:
https://github.com/lathiat/avahi/commit/e111def44a7df4624a4aa3f85fe98054bffb6b4f

I have only performed basic validation so far, however the following scapy query now fails:
send(IP(src="1.1.1.1",dst="DEST_IP")/UDP(sport=53, dport=5353)/DNS(rd=1,qd=DNSQR(qtype="PTR", qname="_ssh._tcp.local.")))

And the following legitimate legacy unicast query still works:
dig HOSTNAME.local @DEST_IP -p 5353


Note that for the test scapy to work, you have to publish an _ssh._tcp service, e.g. put the example ssh.service into /etc/avahi/services. To avoid that, you can query for the machine's mdns hostname as an A record instead.
send(IP(src="1.1.1.1",dst="DEST_IP")/UDP(sport=53, dport=5353)/DNS(rd=1,qd=DNSQR(qtype="A", qname="HOSTNAME.local.")))

Comment 4 Riccardo Schirone 2019-01-02 13:35:50 UTC

This appears to be a duplicate of CVE-2017-6519.

Comment 5 Riccardo Schirone 2019-01-02 14:21:37 UTC

Setting Availability in CVSSv3 to Low because of the rate-limiting feature enabled by default in Avahi, that allows to generate a maximum of 1000 packets per second (which can be configured with the ratelimit-interval-usec and ratelimit-burst options in /etc/avahi/avahi-daemon.conf)

Comment 6 Riccardo Schirone 2019-01-02 14:24:19 UTC

Mitigation:

Ensure UDP port 5353 is blocked in the firewall. Moreover, configure correctly the rate limiting options based on your needs (see ratelimit-interval-usec and ratelimit-burst options in /etc/avahi/avahi-daemon.conf).

Comment 7 Riccardo Schirone 2019-01-03 09:57:37 UTC

Requested MITRE to mark this CVE as a duplicate of CVE-2017-6519.

Comment 8 Riccardo Schirone 2019-01-31 08:18:03 UTC

This flaw has been rejected by MITRE as a duplicate of CVE-2017-6519.

*** This bug has been marked as a duplicate of bug 1426712 ***

Comment 10 Doran Moppert 2020-02-10 04:36:18 UTC

Statement:

This flaw was found to be a duplicate of CVE-2017-6519. Please see https://access.redhat.com/security/cve/CVE-2017-6519 for information about affected products and security errata.