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.
Created avahi tracking bugs for this issue:
Affects: fedora-all [bug 1661253]
This looks to be CVE-2018-1000845.
I have pushed a fix upstream for the issue here:
I have only performed basic validation so far, however the following scapy query now fails:
send(IP(src="126.96.36.199",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="188.8.131.52",dst="DEST_IP")/UDP(sport=53, dport=5353)/DNS(rd=1,qd=DNSQR(qtype="A", qname="HOSTNAME.local.")))
This appears to be a duplicate of CVE-2017-6519.
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)
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).
Requested MITRE to mark this CVE as a duplicate of CVE-2017-6519.
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 ***