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
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: 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.")))
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)
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).
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 ***
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.