A flaw was found in dnsmasq before version 2.83. When receiving a query, dnsmasq does not check for an existing pending request for the same name and forwards a new request. By default, a maximum of 150 pending queries can be sent to upstream servers, so there can be at most 150 queries for the same name. This flaw allows an off-path attacker on the network to substantially reduce the number of attempts that it would have to perform to forge a reply and have it accepted by dnsmasq. This issue is mentioned in the "Birthday Attacks" section of RFC5452. 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.

References

• https://nvd.nist.gov/vuln/detail/CVE-2020-25686
• https://bugzilla.redhat.com/show_bug.cgi?id=1890125
• https://lists.fedoraproject.org/archives/list/package-announce@lists.fedoraproject.org/message/QGB7HL3OWHTLEPSMLDGOMXQKG3KM2QME/
• https://lists.fedoraproject.org/archives/list/package-announce@lists.fedoraproject.org/message/WYW3IR6APUSKOYKL5FT3ACTIHWHGQY32/
• https://security.gentoo.org/glsa/202101-17
• https://www.arista.com/en/support/advisories-notices/security-advisories/12135-security-advisory-61
• https://www.debian.org/security/2021/dsa-4844
• https://www.jsof-tech.com/disclosures/dnspooq/