CVE-2020-27838: A flaw was found in keycloak in versions prior to 13.0.0

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MEDIUM 6.5WATCHLISTUPGRADEDOWNGRADE

CVE-2020-27838 is a medium-severity flaw (CVSS 6.5) affecting keycloak, single sign-on. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

A flaw was found in keycloak in versions prior to 13.0.0. The client registration endpoint allows fetching information about PUBLIC clients (like client secret) without authentication which could be an issue if the same PUBLIC client changed to CONFIDENTIAL later. The highest threat from this vulnerability is to data confidentiality.

Why this priority

EPSS top 3%: very likely to be exploited
On your watchlist

A fixed release or distro patch exists.

Risk facts

CVSS score	6.5 (Medium)
Attack vector	Network (remote)
Attack complexity	Low
Privileges needed	None
User interaction	Required
EPSS exploit chance	17.9% (top 3%)
CISA exploited list	No
Weakness	CWE-287
Published	2021-03-08
Last modified	2026-06-17

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

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

Am I affected?

Timeline

2021-03-08 22:15 UTCPublished CVE record published
2026-06-17 03:09 UTCUpdated Record last modified

redhat keycloak UPGRADE

Affected: < 13.0.0

Fixed in: 13.0.0

Safe to downgrade to: no unaffected older release

1. Check installed version

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

2. UPGRADE to 13.0.0 (Debian / Ubuntu)

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

2. UPGRADE (RHEL / Amazon Linux / Fedora)

sudo dnf upgrade keycloak

Note

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

redhat single sign-on DOWNGRADE

Affected: 7.0

Fixed in: no fixed release known

Safe to downgrade to: a release before 7.0

1. Check installed version

apt-cache policy single-sign-on || rpm -q single-sign-on || single-sign-on --version

2. No fixed release: DOWNGRADE to a release before 7.0 (Debian / Ubuntu)

apt-cache madison single-sign-on sudo apt install single-sign-on=<VERSION_BEFORE_7.0> sudo apt-mark hold single-sign-on

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

dnf --showduplicates list single-sign-on sudo dnf downgrade single-sign-on-<VERSION_BEFORE_7.0> sudo dnf versionlock add single-sign-on

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.

Public exploits and detection

Public code exists for this CVE. Treat unpatched systems as at risk, and only run PoCs in a lab.

Nuclei scan template: KeyCloak - Information 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-2020-27838?

keycloak: upgrade to 13.0.0; single sign-on: downgrade or apply the listed mitigation. Exact commands for each OS are on this page.

Is CVE-2020-27838 being exploited?

CVE-2020-27838 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-2020-27838 affect?

CVE-2020-27838 affects keycloak, single sign-on. Severity is medium (CVSS 6.5). A flaw was found in keycloak in versions prior to 13.0.0. The client registration endpoint allows fetching information about PUBLIC clients (like client secret) without authentication which could be an issue if the same PUBLIC client change

How urgent is CVE-2020-27838?

Priority 52/100. EPSS top 3%: very likely to be exploited; On your watchlist

Software pages

Keycloak vulnerabilities

Related CVEs

CVE-2023-6927 MEDIUM 4.6 MITIGATE DOWNGRADE A flaw was found in Keycloak
CVE-2023-6563 HIGH 7.7 UPGRADE DOWNGRADE An unconstrained memory consumption vulnerability was discovered in Keycloak
CVE-2023-6291 HIGH 7.1 UPGRADE DOWNGRADE A flaw was found in the redirect_uri validation logic in Keycloak
CVE-2023-6134 MEDIUM 4.6 UPGRADE UPGRADE A flaw was found in Keycloak that prevents certain schemes in redirects, but permits them if a wildcard is app
CVE-2025-8419 MEDIUM 5.3 MITIGATE A vulnerability was found in Keycloak-services

References

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