What’s Vulnerable › Vulnerabilities

CVE-2020-25685

• Severity: low (CVSS 3.7 v3.1)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 2.2% probability of exploitation in the next 30 days
• Public exploit or detection template: none known
• Published: 2021-01-20 · updated 2026-06-17
• Weakness: CWE-326

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.

Affected products

• Arista Networks EOS: from 4.21 before 4.21.14m; from 4.22 before 4.22.9m; from 4.23 before 4.23.7m; from 4.24 before 4.24.5m; from 4.25 before 4.25.2f — fixed in 4.21.14m, 4.22.9m, 4.23.7m, 4.24.5m, 4.25.2f
• Debian Linux: 10.0
• Fedoraproject Fedora: 32, 33
• Simon Kelley dnsmasq: before 2.83 — fixed in 2.83

How to fix

Upgrade to a fixed version: Arista Networks EOS 4.21.14m, 4.22.9m, 4.23.7m, 4.24.5m; Simon Kelley dnsmasq 2.83. Check the vendor advisory for mitigations.

References

• https://bugzilla.redhat.com/show_bug.cgi?id=1889688
• https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/QGB7HL3OWHTLEPSMLDGOMXQKG3KM2QME/
• https://lists.fedoraproject.org/archives/list/package-announce%40lists.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/
• https://bugzilla.redhat.com/show_bug.cgi?id=1889688
• https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/QGB7HL3OWHTLEPSMLDGOMXQKG3KM2QME/
• https://lists.fedoraproject.org/archives/list/package-announce%40lists.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

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