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Fencer Vulns
medium 5.3

CVE-2021-3424 json

Keycloak is vulnerable to IDN homograph attack

published 2021-06-01 5 y ago modified 2026-06-17 4 mo ago also GHSA-pf38-cw3p-22q9 , EUVD-2022-1798

cvss
5.3
version 3.1, NVD
cisa kev
Not listed
not in CISA's catalog
epss
0.8%
EPSS 0.8% chance of exploitation in 30 days, percentile 55%
public exploits
0
none known

Summary

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.

Patch / fix

  • maven org.keycloak:keycloak-services 18.0.0
  • rh-sso7-keycloak red hat single sign on 7 9.0.13-1.redhat_00006.1.el8sso
  • rh-sso7-keycloak-server red hat single sign on 7 9.0.13-1.redhat_00006.1.el8sso
  • rh-sso7-keycloak red hat single sign on 7 9.0.13-1.redhat_00006.1.el7sso
  • rh-sso7-keycloak-server red hat single sign on 7 9.0.13-1.redhat_00006.1.el7sso
  • rh-sso7-keycloak red hat single sign on 7 9.0.13-1.redhat_00006.1.el6sso
  • rh-sso7-keycloak-server red hat single sign on 7 9.0.13-1.redhat_00006.1.el6sso

red hat advisories RHSA-2021:2065RHSA-2021:2064RHSA-2021:2063

  • keycloak Arch Linux 16.0.0-1

arch linux advisories AVG-1332

Vendor advisories

What the vendors themselves say about their products: affected, fixed or not affected, and what to do.

red hat product security vex CVE-2021-3424 updated cvss 5.3

keycloak: Internationalized domain name (IDN) homograph attack to impersonate users

  • Red Hat Single Sign-On 7.4 for RHEL 6 Server rh-sso7-keycloak 9.0.13-1.redhat_00006.1.el6sso, rh-sso7-keycloak-server 9.0.13-1.redhat_00006.1.el6sso
    fixed: vendor fix RHSA-2021:2063
  • Red Hat Single Sign-On 7.4 for RHEL 7 Server rh-sso7-keycloak 9.0.13-1.redhat_00006.1.el7sso, rh-sso7-keycloak-server 9.0.13-1.redhat_00006.1.el7sso
    fixed: vendor fix RHSA-2021:2064
  • Red Hat Single Sign-On 7.4 for RHEL 8 rh-sso7-keycloak 9.0.13-1.redhat_00006.1.el8sso, rh-sso7-keycloak-server 9.0.13-1.redhat_00006.1.el8sso
    fixed: vendor fix RHSA-2021:2065
  • Red Hat Single Sign-On 7.4.7
    fixed: vendor fix RHSA-2021:2070
  • Red Hat Decision Manager 7 keycloak keycloak Red Hat Fuse 7 keycloak keycloak Red Hat Integration Camel K 1 keycloak keycloak Red Hat OpenShift Application Runtimes keycloak keycloak Red Hat Process Automation 7 keycloak keycloak Red Hat support for Spring Boot keycloak keycloak
    not affected: vulnerable code not present

Red Hat CSAF VEX © Red Hat, Inc., from https://security.access.redhat.com/data/csaf/v2/vex/; changed: reduced to product statuses and remediations. CC BY 4.0 · csaf

Exploit prediction

0.77% chance of exploitation in the next 30 days, higher than 55% of all scored CVEs (FIRST EPSS, 2026-11-08).

CVSS scores

assigned by version score vector
NVD 3.1 5.3 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N
NVD 2.0 5.0 AV:N/AC:L/Au:N/C:N/I:P/A:N
GitHub 3.1 5.3 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N

Affected packages

ecosystem package affected fixed in
maven org.keycloak:keycloak-services
<18.0.0
18.0.0

Affected products

  • n/a keycloak

Classification

Weakness

References

Sources

Fencer Vulns keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.