CVE-2019-19331: knot-resolver before version 4.3.0 is vulnerable to denial of service through high CPU utilization

Q: How do I fix CVE-2019-19331?

knot resolver: upgrade to 4.3.0; debian linux: mitigate or apply the listed mitigation. Exact commands for each OS are on this page.

Q: Is CVE-2019-19331 being exploited?

CVE-2019-19331 is not on the CISA Known Exploited Vulnerabilities list at the time of the last update. Check again, as this can change.

Q: What does CVE-2019-19331 affect?

CVE-2019-19331 affects knot resolver, debian linux. Severity is high (CVSS 7.5). knot-resolver before version 4.3.0 is vulnerable to denial of service through high CPU utilization. DNS replies with very many resource records might be processed very inefficiently, in extreme cases taking even several CPU seconds for each

Q: How urgent is CVE-2019-19331?

Priority 62/100. High severity; Public exploit reference; Remotely exploitable, no login, no user action; On your watchlist

This week

HIGH 7.5REMOTEWATCHLISTUPGRADEMITIGATE

CVE-2019-19331 is a high-severity flaw (CVSS 7.5) affecting knot resolver, debian linux. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

knot-resolver before version 4.3.0 is vulnerable to denial of service through high CPU utilization. DNS replies with very many resource records might be processed very inefficiently, in extreme cases taking even several CPU seconds for each such uncached message. For example, a few thousand A records can be squashed into one DNS message (limit is 64kB).

Why this priority

High severity
Public exploit reference
Remotely exploitable, no login, no user action
On your watchlist

A fixed release or distro patch exists.

Risk facts

CVSS score	7.5 (High)
Attack vector	Network (remote)
Attack complexity	Low
Privileges needed	None
User interaction	None
EPSS exploit chance	2.1% (top 18%)
CISA exploited list	No
Weakness	CWE-407, CWE-404
Published	2019-12-16
Last modified	2026-06-17

Publisher (CNA): Red Hat, Inc. · Vendor: debian · nic

Last updated 2026-06-17 · Sources: CVE Program, NVD, CISA KEV, EPSS and vendor advisories · How we score

Am I affected?

Timeline

2019-12-16 16:15 UTCPublished CVE record published
2026-06-17 02:26 UTCUpdated Record last modified

nic knot resolver UPGRADE

Affected: < 4.3.0

Fixed in: 4.3.0

Safe to downgrade to: no unaffected older release

1. Check installed version

apt-cache policy knot-resolver || rpm -q knot-resolver || knot-resolver --version

2. UPGRADE to 4.3.0 (Debian / Ubuntu)

sudo apt update && sudo apt install --only-upgrade knot-resolver

2. UPGRADE (RHEL / Amazon Linux / Fedora)

sudo dnf upgrade knot-resolver

Note

Distros often backport fixes without changing the version number. Confirm with the distro advisory or changelog.

debian debian linux MITIGATE

Affected: 10.0

Fixed in: no fixed release known

Safe to downgrade to: a release before 10.0

Check your OS release

cat /etc/os-release; uname -r

Debian / Ubuntu

sudo apt update && sudo apt full-upgrade

RHEL / Amazon Linux / Fedora

sudo dnf upgrade --refresh

Windows

Install the latest cumulative update from Windows Update

If no patch exists yet

OS downgrades are not safe. Apply the vendor mitigation from the advisory and restrict exposure.

Verify at the official source NVD · CVE Program · Report a problem with this page
Scores and fixes here are computed automatically from those and other public sources. Confirm with the vendor advisory before changing production systems.

Quick answers

How do I fix CVE-2019-19331?

knot resolver: upgrade to 4.3.0; debian linux: mitigate or apply the listed mitigation. Exact commands for each OS are on this page.

Is CVE-2019-19331 being exploited?

CVE-2019-19331 is not on the CISA Known Exploited Vulnerabilities list at the time of the last update. Check again, as this can change.

What does CVE-2019-19331 affect?

CVE-2019-19331 affects knot resolver, debian linux. Severity is high (CVSS 7.5). knot-resolver before version 4.3.0 is vulnerable to denial of service through high CPU utilization. DNS replies with very many resource records might be processed very inefficiently, in extreme cases taking even several CPU seconds for each

How urgent is CVE-2019-19331?

Priority 62/100. High severity; Public exploit reference; Remotely exploitable, no login, no user action; On your watchlist

Software pages

Debian vulnerabilities

Related CVEs

CVE-2023-46317 HIGH 7.5 UPGRADE Knot Resolver before 5.7.0 performs many TCP reconnections upon receiving certain nonsensical responses from s
CVE-2023-26249 HIGH 7.5 UPGRADE Knot Resolver before 5.6.0 enables attackers to consume its resources, launching amplification attacks and pot
CVE-2022-40188 HIGH 7.5 UPGRADE MITIGATE Knot Resolver before 5.5.3 allows remote attackers to cause a denial of service (CPU consumption) because of a
CVE-2022-32983 MEDIUM 5.3 UPGRADE Knot Resolver through 5.5.1 may allow DNS cache poisoning when there is an attempt to limit forwarding actions
CVE-2021-40083 HIGH 7.5 UPGRADE Knot Resolver before 5.3.2 is prone to an assertion failure, triggerable by a remote attacker in an edge case

References

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