CVE-2020-5591: XACK DNS 1.11.0 to 1.11.4, 1.10.0 to 1.10.8, 1.8.0 to 1.8.23, 1.7.0 to 1.7.18, and versions before 1.7.0 allow

This month

HIGH 7.5REMOTEUPGRADE

CVE-2020-5591 is a high-severity flaw (CVSS 7.5) affecting xack dns. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

XACK DNS 1.11.0 to 1.11.4, 1.10.0 to 1.10.8, 1.8.0 to 1.8.23, 1.7.0 to 1.7.18, and versions before 1.7.0 allow remote attackers to cause a denial of service condition resulting in degradation of the recursive resolver's performance or compromising the recursive resolver as a reflector in a reflection attack.

Why this priority

High severity
Remotely exploitable, no login, no user action

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	1.6% (top 24%)
CISA exploited list	No
Weakness	CWE-674
Published	2020-06-05
Last modified	2026-06-17

Publisher (CNA): JPCERT/CC · Vendor: xack

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

Am I affected?

Timeline

2020-06-05 18:15 UTCPublished CVE record published
2026-06-17 03:21 UTCUpdated Record last modified

xack xack dns UPGRADE

Affected: <= 1.7.18 · >= 1.8.0 and <= 1.8.23 · >= 1.10.0 and <= 1.10.8 · >= 1.11.0 and <= 1.11.4

Fixed in: newer than 1.11.4

Safe to downgrade to: a release before 1.8.0

1. Check installed version

apt-cache policy xack-dns || rpm -q xack-dns || xack-dns --version

2. UPGRADE to newer than 1.11.4 (Debian / Ubuntu)

sudo apt update && sudo apt install --only-upgrade xack-dns

2. UPGRADE (RHEL / Amazon Linux / Fedora)

sudo dnf upgrade xack-dns

Note

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

3. If no update is available yet, DOWNGRADE to a release before 1.8.0 (Debian / Ubuntu)

apt-cache madison xack-dns sudo apt install xack-dns=<VERSION_BEFORE_1.8.0> sudo apt-mark hold xack-dns

3. If no update is available yet, DOWNGRADE (RHEL / Amazon Linux / Fedora)

dnf --showduplicates list xack-dns sudo dnf downgrade xack-dns-<VERSION_BEFORE_1.8.0> sudo dnf versionlock add xack-dns

Downgrade risk

Downgrading can break dependent software and may reopen older bugs. Read the distro advisory first and test on a non-production host.

After downgrade

Restart the service, and keep the package held until a fixed release ships.

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-2020-5591?

xack dns: upgrade to newer than 1.11.4. Exact commands for each OS are on this page.

Is CVE-2020-5591 being exploited?

CVE-2020-5591 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-2020-5591 affect?

CVE-2020-5591 affects xack dns. Severity is high (CVSS 7.5). XACK DNS 1.11.0 to 1.11.4, 1.10.0 to 1.10.8, 1.8.0 to 1.8.23, 1.7.0 to 1.7.18, and versions before 1.7.0 allow remote attackers to cause a denial of service condition resulting in degradation of the recursive resolver's performance or compr

How urgent is CVE-2020-5591?

Priority 50/100. High severity; Remotely exploitable, no login, no user action

References

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