CVE-2020-12105: OpenConnect through 8.08 mishandles negative return values from X509_check_ function calls, which might assist

Q: How do I fix CVE-2020-12105?

openconnect: upgrade to newer than 8.08; leap: mitigate or apply the listed mitigation. Exact commands for each OS are on this page.

Q: Is CVE-2020-12105 being exploited?

CVE-2020-12105 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-2020-12105 affect?

CVE-2020-12105 affects openconnect, leap. Severity is medium (CVSS 5.9). OpenConnect through 8.08 mishandles negative return values from X509_check_ function calls, which might assist attackers in performing man-in-the-middle attacks.

Q: How urgent is CVE-2020-12105?

Priority 45/100. Remotely exploitable, no login, no user action

This month

MEDIUM 5.9REMOTEUPGRADEMITIGATE

CVE-2020-12105 is a medium-severity flaw (CVSS 5.9) affecting openconnect, leap. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

OpenConnect through 8.08 mishandles negative return values from X509_check_ function calls, which might assist attackers in performing man-in-the-middle attacks.

Why this priority

Remotely exploitable, no login, no user action

A fixed release or distro patch exists.

Risk facts

CVSS score	5.9 (Medium)
Attack vector	Network (remote)
Attack complexity	High
Privileges needed	None
User interaction	None
EPSS exploit chance	1.7% (top 22%)
CISA exploited list	No
Weakness	CWE-755
Published	2020-04-23
Last modified	2026-06-17

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

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

Am I affected?

Timeline

2020-04-23 17:15 UTCPublished CVE record published
2026-06-17 02:51 UTCUpdated Record last modified

infradead openconnect UPGRADE

Affected: <= 8.08

Fixed in: newer than 8.08

Safe to downgrade to: no unaffected older release

1. Check installed version

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

2. UPGRADE to newer than 8.08 (Debian / Ubuntu)

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

2. UPGRADE (RHEL / Amazon Linux / Fedora)

sudo dnf upgrade openconnect

Note

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

opensuse leap MITIGATE

Affected: 15.1

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-2020-12105?

openconnect: upgrade to newer than 8.08; leap: mitigate or apply the listed mitigation. Exact commands for each OS are on this page.

Is CVE-2020-12105 being exploited?

CVE-2020-12105 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-2020-12105 affect?

CVE-2020-12105 affects openconnect, leap. Severity is medium (CVSS 5.9). OpenConnect through 8.08 mishandles negative return values from X509_check_ function calls, which might assist attackers in performing man-in-the-middle attacks.

How urgent is CVE-2020-12105?

Priority 45/100. Remotely exploitable, no login, no user action

Related CVEs

CVE-2020-12823 CRITICAL 9.8 DOWNGRADE MITIGATE OpenConnect 8.09 has a buffer overflow, causing a denial of service (application crash) or possibly unspecifie
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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