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MEDIUM severity

CVE-2021-3424 — keycloak-services

MEDIUM

CVE-2021-3424 is a medium-severity (CVSS 5.3) Improper Authentication vulnerability in org.keycloak:keycloak-services. A fix is available for org.keycloak:keycloak-services — see the affected versions and patch details below.

Keycloak is vulnerable to IDN homograph attack

Published
Updated
Affected
1 pkg
Patched
1 / 1
Exploits
None indexed
Exploitation data as of Nov 6, 2026 · OSV.dev, NVD, FIRST.org (EPSS)

EPSS Exploitation Probability

via FIRST.org ↗
0.8%probability of exploitation in next 30 days
Lower Risk0.00%
Lower risk than most CVEs56th percentile — riskier than 56% of all scored CVEsHighest risk
0.00%0.42%0.85%1.27%0.2%0.8%May 26Sep 26Nov 26

Probability of exploitation in the next 30 days, from FIRST.org EPSS.

How urgent is this, really

Where this sits among everything scored

Real-World Exposure

1 pkg affected
☕org.keycloak:keycloak-services

Real-time download stats are indexed for npm and PyPI packages. This vulnerability affects Maven packages — download data is not available via public APIs for these ecosystems.

Description

A flaw was found in keycloak as shipped in Red Hat Single Sign-On 7.4 where IDN homograph attacks are possible. A malicious user can register himself with a name already registered and trick admin to grant him extra privileges.

Affected Packages

1 total 1 fixed
EcosystemPackageVulnerable rangeFix
☕Mavenorg.keycloak:keycloak-servicesall versions18.0.0org.keycloak:keycloak-services:18.0.0

Affected Products

1 product · 1 configurations
Application
single sign-onredhat
1 version
7.4

Detection & mitigation playbook

Open-source dependency

  1. Detect

    Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for org.keycloak:keycloak-services, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.

  2. Fix

    Update org.keycloak:keycloak-services to 18.0.0 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2021-3424 is resolved across your whole dependency graph.

  3. Workarounds

    Put an independent control in front of the weakness: restrict the affected endpoint or interface to trusted networks, require an additional authentication factor or proxy-level check, and invalidate existing sessions and credentials in case the flaw has already been used.

Fixing This On Your OS

If you run this on a Linux distribution, patch through your package manager against the distro's own security advisory below — it tracks the exact backported fix for your release, which can ship on a different timeline (and sometimes a different severity) than the upstream project.

Red HatLow
ProductFixed inAdvisory
Red Hat Single Sign-On 7.4.7see advisoryRHSA-2021:2070
Red Hat Single Sign-On 7.4 for RHEL 6rh-sso7-keycloak-0:9.0.13-1.redhat_00006.1.el6ssoRHSA-2021:2063
Red Hat Single Sign-On 7.4 for RHEL 7rh-sso7-keycloak-0:9.0.13-1.redhat_00006.1.el7ssoRHSA-2021:2064
Red Hat Single Sign-On 7.4 for RHEL 8rh-sso7-keycloak-0:9.0.13-1.redhat_00006.1.el8ssoRHSA-2021:2065

Frequently Asked Questions

A flaw was found in keycloak as shipped in Red Hat Single Sign-On 7.4 where IDN homograph attacks are possible. A malicious user can register himself with a name already registered and trick admin to grant him extra privileges.
O3 Security · Impact-Aware SCA

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CVE-2021-3424: keycloak-services — Fixed in 18.0.0