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 Package

OS OS Version Package Name Package Version
ubuntu upstream dnsmasq 2.82-1ubuntu2
ubuntu 18.04 dnsmasq 2.79-1ubuntu0.2
ubuntu 20.04 dnsmasq 2.80-1.1ubuntu1.2
ubuntu 20.10 dnsmasq 2.82-1ubuntu1.1
ubuntu 21.10 dnsmasq 2.82-1ubuntu2
ubuntu 22.04 dnsmasq 2.82-1ubuntu2
ubuntu upstream dnsmasq 2.82-1ubuntu2
ubuntu 14.04 dnsmasq any
ubuntu upstream dnsmasq 2.83
ubuntu 16.04 dnsmasq 2.75-1ubuntu0.16.04.7
ubuntu upstream dnsmasq 2.82-1ubuntu2