CVE-2020-25685

Description

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.

How to fix CVE-2020-25685

To remediate CVE-2020-25685, upgrade the affected package to a fixed version below.

• —upgrade to 2.83-r0 or later
• —upgrade to 2.83-1 or later

Is CVE-2020-25685 being exploited?

Low — EPSS is 0.4%, meaning exploitation activity has not been observed at scale.

Affected packages (2)

• from 0, < 2.83-r0
• from 0, < 2.83-1

CVSS scores

References (2)

• ADVISORYsecurity.alpinelinux.org/vuln/CVE-2020-25685
• ADVISORYsecurity-tracker.debian.org/tracker/CVE-2020-25685