CVE-2021-20231: A flaw was found in gnutls

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CRITICAL 9.8REMOTEWATCHLISTUPGRADEMITIGATEMITIGATE

CVE-2021-20231 is a critical-severity flaw (CVSS 9.8) affecting gnutls, enterprise linux, fedora. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

A flaw was found in gnutls. A use after free issue in client sending key_share extension may lead to memory corruption and other consequences.

Why this priority

Critical 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	9.8 (Critical)
Attack vector	Network (remote)
Attack complexity	Low
Privileges needed	None
User interaction	None
EPSS exploit chance	3.6% (top 10%)
CISA exploited list	No
Weakness	CWE-416
Published	2021-03-12
Last modified	2026-10-14

Publisher (CNA): Red Hat, Inc. · Vendor: fedoraproject · gnu · netapp · redhat

Last updated 2026-10-14 · Sources: CVE Program, NVD, CISA KEV, EPSS and vendor advisories · How we score

Am I affected?

Timeline

2021-03-12 19:15 UTCPublished CVE record published
2026-10-14 11:16 UTCUpdated Record last modified

gnu gnutls UPGRADE

Affected: >= 3.6.3 and < 3.7.1

Fixed in: 3.7.1

Safe to downgrade to: a release before 3.6.3

1. Check installed version

apt-cache policy gnutls || rpm -q gnutls || gnutls --version

2. UPGRADE to 3.7.1 (Debian / Ubuntu)

sudo apt update && sudo apt install --only-upgrade gnutls

2. UPGRADE (RHEL / Amazon Linux / Fedora)

sudo dnf upgrade gnutls

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 3.6.3 (Debian / Ubuntu)

apt-cache madison gnutls sudo apt install gnutls=<VERSION_BEFORE_3.6.3> sudo apt-mark hold gnutls

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

dnf --showduplicates list gnutls sudo dnf downgrade gnutls-<VERSION_BEFORE_3.6.3> sudo dnf versionlock add gnutls

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.

redhat enterprise linux MITIGATE

Affected: 8.0

Fixed in: no fixed release known

Safe to downgrade to: a release before 8.0

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.

fedoraproject fedora MITIGATE

Affected: 34

Fixed in: no fixed release known

Safe to downgrade to: a release before 34

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.

netapp active iq unified manager MITIGATE

Affected: all versions

Fixed in: no fixed release known

Safe to downgrade to: no unaffected older release

1. Check installed version

apt-cache policy active-iq-unified-manager || rpm -q active-iq-unified-manager || active-iq-unified-manager --version

No fixed or unaffected release known

Apply the vendor mitigation from the advisory, disable the affected feature, or restrict network access.

netapp e-series performance analyzer MITIGATE

Affected: all versions

Fixed in: no fixed release known

Safe to downgrade to: no unaffected older release

1. Check installed version

apt-cache policy e-series-performance-analyzer || rpm -q e-series-performance-analyzer || e-series-performance-analyzer --version

No fixed or unaffected release known

Apply the vendor mitigation from the advisory, disable the affected feature, or restrict network access.

Exact fixes by distribution

A distro patch exists: prefer upgrading over downgrading.

Fedora 46 · keepalived · FIXED · 2.4.3-1.fc46 · FEDORA-2026-0c83a077d7 · source

sudo dnf upgrade --advisory=FEDORA-2026-0c83a077d7

Fedora ELN · dracut · FIXED · 111-5.eln159 · FEDORA-2026-982407d9e3 · source

sudo dnf upgrade --advisory=FEDORA-2026-982407d9e3

Ubuntu 20.04 · gnutls28 · FIXED · 3.6.13-2ubuntu1.6

sudo apt update && sudo apt install --only-upgrade gnutls28 dpkg --compare-versions "$(dpkg-query -W -f='${Version}' gnutls28)" ge "3.6.13-2ubuntu1.6" && echo PATCHED || echo STILL-VULNERABLE

Ubuntu 22.04 · gnutls28 · NOT AFFECTED

Debian 12 · gnutls28 · FIXED · 3.7.1-1

sudo apt update && sudo apt install --only-upgrade gnutls28 dpkg --compare-versions "$(dpkg-query -W -f='${Version}' gnutls28)" ge "3.7.1-1" && echo PATCHED || echo STILL-VULNERABLE

Debian 13 · gnutls28 · FIXED · 3.7.1-1

sudo apt update && sudo apt install --only-upgrade gnutls28 dpkg --compare-versions "$(dpkg-query -W -f='${Version}' gnutls28)" ge "3.7.1-1" && echo PATCHED || echo STILL-VULNERABLE

RHEL 8 · gnutls · FIXED · gnutls-3.6.16-4.el8

sudo dnf upgrade --advisory=RHSA-2021:4451 rpm -q gnutls

RHEL 8 · nettle · FIXED · nettle-3.4.1-7.el8

sudo dnf upgrade --advisory=RHSA-2021:4451 rpm -q nettle

RHEL 6 · gnutls · NOT AFFECTED

RHEL 7 · gnutls · NOT AFFECTED

RHEL 9 · gnutls · NOT AFFECTED

Alpine 3.20 · gnutls · FIXED · gnutls-3.7.1-r0

apk add --upgrade gnutls apk info -v gnutls

Alpine 3.21 · gnutls · FIXED · gnutls-3.7.1-r0

apk add --upgrade gnutls apk info -v gnutls

Alpine 3.22 · gnutls · FIXED · gnutls-3.7.1-r0

apk add --upgrade gnutls apk info -v gnutls

Alpine 3.23 · gnutls · FIXED · gnutls-3.7.1-r0

apk add --upgrade gnutls apk info -v gnutls

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-2021-20231?

gnutls: upgrade to 3.7.1; enterprise linux: mitigate or apply the listed mitigation; fedora: mitigate or apply the listed mitigation. Exact commands for each OS are on this page.

Is CVE-2021-20231 being exploited?

CVE-2021-20231 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-2021-20231 affect?

CVE-2021-20231 affects gnutls, enterprise linux, fedora. Severity is critical (CVSS 9.8). A flaw was found in gnutls. A use after free issue in client sending key_share extension may lead to memory corruption and other consequences.

How urgent is CVE-2021-20231?

Priority 72/100. Critical severity; Public exploit reference; Remotely exploitable, no login, no user action; On your watchlist

Software pages

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References

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