DNS amplification attack in Knot Resolver

1) Resource exhaustion

EUVDB-ID: #VU29248

Risk: Medium

CVSSv4.0: 6.6 [CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N/E:U/U:Green]

CVE-ID: CVE-2020-12667

CWE-ID: CWE-400 - Resource exhaustion

Exploit availability: No

Description

The vulnerability allows a remote attacker to perform a denial of service (DoS) attack.

The vulnerability exists due to application does not properly control consumption of internal resources when processing NSDNAME in NS records. A remote attacker can perform traffic amplification via a crafted DNS answer from an attacker-controlled server. This vulnerability is dubbed "NXNSAttack".

Mitigation

Install updates from vendor's website.

Vulnerable software versions

Knot Resolver: 1.0 - 5.1.0

CPE2.3

• cpe:2.3:a:nic:knot_resolver:1.0:*:*:*:*:*:*:*
• cpe:2.3:a:nic:knot_resolver:1.0.0:*:*:*:*:*:*:*
• cpe:2.3:a:nic:knot_resolver:1.1:*:*:*:*:*:*:*

External links

https://cyber-security-group.cs.tau.ac.il/#
https://www.openwall.com/lists/oss-security/2020/05/19/2
https://en.blog.nic.cz/2020/05/19/nxnsattack-upgrade-resolvers-to-stop-new-kind-of-random-subdomain-attack/
https://lists.fedoraproject.org/archives/list/package-announce@lists.fedoraproject.org/message/76Y4FITMOH6RVPWAANGV7NB2ZHPJJGDQ/
https://www.knot-resolver.cz/2020-05-19-knot-resolver-5.1.1.html

Q & A

Can this vulnerability be exploited remotely?

Yes. This vulnerability can be exploited by a remote non-authenticated attacker via the Internet.

Is there known malware, which exploits this vulnerability?

No. We are not aware of malware exploiting this vulnerability.