CVE-2020-25685

Published: 19 January 2021

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.

Priority

Medium

CVSS 3 base score: 3.7

Status

Package Release Status
dnsmasq
Launchpad, Ubuntu, Debian
Upstream
Released (2.83)
Ubuntu 21.04 (Hirsute Hippo)
Released (2.82-1ubuntu2)
Ubuntu 20.10 (Groovy Gorilla)
Released (2.82-1ubuntu1.1)
Ubuntu 20.04 LTS (Focal Fossa)
Released (2.80-1.1ubuntu1.2)
Ubuntu 18.04 LTS (Bionic Beaver)
Released (2.79-1ubuntu0.2)
Ubuntu 16.04 LTS (Xenial Xerus)
Released (2.75-1ubuntu0.16.04.7)
Ubuntu 14.04 ESM (Trusty Tahr) Needs triage