Spoofing attack in Keycloak - CVE-2021-3424
Published: May 25, 2021 / Updated: June 29, 2026
Vulnerability identifier: #VU53529
CSH Severity: Medium
CVSS v4: 6.9 [CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:L/VA:N/SC:N/SI:N/SA:N]
CVE-ID: CVE-2021-3424
CWE-ID: CWE-451
Exploitation vector: Remote access
Exploit availability:
No public exploit available
Vulnerability details
The vulnerability allows a remote attacker to perform spoofing attack.
The vulnerability exists due to incorrect processing of user IDN names. A remote attacker can register with an IDN name, which looks exactly like a name of previously registered user and trick the application administrator into assigning higher privileges to such account.
Affected software
Keycloak
Red Hat Single Sign-On
rh-sso7-keycloak (Red Hat package)
Red Hat Single Sign-On
rh-sso7-keycloak (Red Hat package)
How to mitigate CVE-2021-3424
Install update from vendor's website.
Keycloak - update to 18.0.0
Red Hat Single Sign-On - update to 7.4.7
rh-sso7-keycloak (Red Hat package) - addressed in versions 9.0.13-1.redhat_00006.1.el6sso, 9.0.13-1.redhat_00006.1.el7sso, 9.0.13-1.redhat_00006.1.el8sso
Red Hat Single Sign-On - update to 7.4.7
rh-sso7-keycloak (Red Hat package) - addressed in versions 9.0.13-1.redhat_00006.1.el6sso, 9.0.13-1.redhat_00006.1.el7sso, 9.0.13-1.redhat_00006.1.el8sso