A flaw was found in dnsmasq before version 2.83. When getting a reply from a forwarded query, dnsmasq checks in forward.c:reply_query(), which is the forwarded query that matches the reply, by only using a weak hash of the query name. Due to the weak hash (CRC32 when dnsmasq is compiled without DNSSEC, SHA-1 when it is) this flaw allows an off-path attacker to find several different domains all having the same hash, substantially reducing the number of attempts they would have to perform to forge a reply and get it accepted by dnsmasq. This is in contrast with RFC5452, which specifies that the query name is one of the attributes of a query that must be used to match a reply. This flaw could be abused to perform a DNS Cache Poisoning attack. If chained with CVE-2020-25684 the attack complexity of a successful attack is reduced. The highest threat from this vulnerability is to data integrity.

Affected Software

CPE Name Name Version
thekelleys:dnsmasq thekelleys dnsmasq 2.83
fedoraproject:fedora fedoraproject fedora 32
fedoraproject:fedora fedoraproject fedora 33
debian:debian_linux debian debian linux 10.0
arista:eos arista eos 4.21.14m
arista:eos arista eos 4.22.9m
arista:eos arista eos 4.23.7m
arista:eos arista eos 4.24.5m
arista:eos arista eos 4.25.2f