CVE-2020-25685: Weak Encryption
A flaw was found in dnsmasq before version 2.83. When getting a reply from a forwarded query, dnsmasq checks in forward.c:replyquery(), 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.
Other sources
When getting a reply from a forwarded query, dnsmasq checks in forward.c:replyquery() which one 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) an attacker can find several different domains all having the same hash, substantially reducing the number of attempts he would have to perform to forge a reply and get it accepted by dnsmasq. This is in contrast with RFC5452, which specifies that 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.
— Red Hat
Affected Software
Remediation
Patch Available
Event History
Frequently Asked Questions
What is CVE-2020-25685?
CVE-2020-25685 is a vulnerability in dnsmasq before version 2.83 that allows remote attackers to bypass DNSSEC validation.
How does CVE-2020-25685 impact dnsmasq?
CVE-2020-25685 allows attackers to exploit a weak hash function in dnsmasq, potentially leading to DNS cache poisoning.
Which versions of dnsmasq are affected by CVE-2020-25685?
Versions of dnsmasq older than 2.83 are affected by CVE-2020-25685.
What is the severity of CVE-2020-25685?
CVE-2020-25685 has a severity rating of medium, with a CVSS score of 3.7.
How can I mitigate CVE-2020-25685?
To mitigate CVE-2020-25685, update dnsmasq to version 2.83 or later.