The Avahi daemon in Avahi before 0.6.20 allows attackers to cause a denial of service (exit) via empty TXT data over D-Bus, which triggers an assert error.
The consume_labels function in avahi-core/dns.c in Avahi before 0.6.16 allows remote attackers to cause a denial of service (infinite loop) via a crafted compressed DNS response with a label that points to itself.
Avahi before 0.6.15 does not verify the sender identity of netlink messages to ensure that they come from the kernel instead of another process, which allows local users to spoof network changes to Avahi.