CVE-2020-12823: OpenConnect 8.09 has a buffer overflow, causing a denial of service (application crash) or possibly unspecifie

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CRITICAL 9.8REMOTEWATCHLISTDOWNGRADEMITIGATEMITIGATE

CVE-2020-12823 is a critical-severity flaw (CVSS 9.8) affecting openconnect, fedora, debian linux. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

OpenConnect 8.09 has a buffer overflow, causing a denial of service (application crash) or possibly unspecified other impact, via crafted certificate data to get_cert_name in gnutls.c.

Why this priority

Critical severity
EPSS top 8%: very likely to be exploited
Public exploit reference
Remotely exploitable, no login, no user action
On your watchlist

No fix is published yet: follow the downgrade or mitigation steps.

Risk facts

CVSS score	9.8 (Critical)
Attack vector	Network (remote)
Attack complexity	Low
Privileges needed	None
User interaction	None
EPSS exploit chance	4.7% (top 8%)
CISA exploited list	No
Weakness	CWE-120
Published	2020-05-12
Last modified	2026-06-17

Publisher (CNA): MITRE · Vendor: debian · fedoraproject · infradead · opensuse

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

Am I affected?

Timeline

2020-05-12 18:15 UTCPublished CVE record published
2026-06-17 02:52 UTCUpdated Record last modified

infradead openconnect DOWNGRADE

Affected: 8.09

Fixed in: no fixed release known

Safe to downgrade to: a release before 8.09

1. Check installed version

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

2. No fixed release: DOWNGRADE to a release before 8.09 (Debian / Ubuntu)

apt-cache madison openconnect sudo apt install openconnect=<VERSION_BEFORE_8.09> sudo apt-mark hold openconnect

2. No fixed release: DOWNGRADE (RHEL / Amazon Linux / Fedora)

dnf --showduplicates list openconnect sudo dnf downgrade openconnect-<VERSION_BEFORE_8.09> sudo dnf versionlock add openconnect

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.

fedoraproject fedora MITIGATE

Affected: 30 · 31 · 32

Fixed in: no fixed release known

Safe to downgrade to: a release before 30

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.

debian debian 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.

opensuse leap MITIGATE

Affected: 15.1 · 15.2

Fixed in: no fixed release known

Safe to downgrade to: a release before 15.1

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-2020-12823?

openconnect: downgrade or apply the listed mitigation; fedora: mitigate or apply the listed mitigation; debian linux: mitigate or apply the listed mitigation. Exact commands for each OS are on this page.

Is CVE-2020-12823 being exploited?

CVE-2020-12823 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-2020-12823 affect?

CVE-2020-12823 affects openconnect, fedora, debian linux. Severity is critical (CVSS 9.8). OpenConnect 8.09 has a buffer overflow, causing a denial of service (application crash) or possibly unspecified other impact, via crafted certificate data to get_cert_name in gnutls.c.

How urgent is CVE-2020-12823?

Priority 72/100. Critical severity; EPSS top 8%: very likely to be exploited; Public exploit reference; Remotely exploitable, no login, no user action; On your watchlist

Software pages

Debian vulnerabilities · GnuTLS vulnerabilities

Related CVEs

CVE-2020-12105 MEDIUM 5.9 UPGRADE MITIGATE OpenConnect through 8.08 mishandles negative return values from X509_check_ function calls, which might assist
CVE-2013-7098 CRITICAL 9.8 UPGRADE OpenConnect VPN client with GnuTLS before 5.02 contains a heap overflow if MTU is increased on reconnection.

References

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