CVE-2023-0105: Redhat Keycloak Auth Bypass Vulnerability

CVE-2023-0105 Overview

A critical flaw was discovered in Red Hat Keycloak that allows attackers to impersonate or lock out legitimate users due to improper handling of email trust. This authentication bypass vulnerability enables malicious actors to "shadow" other users by registering accounts with the same email address, potentially leading to account takeover or denial of service conditions for affected users.

Critical Impact

Attackers can impersonate legitimate users or cause account lockouts by exploiting improper email trust validation in Keycloak, affecting identity management across applications relying on Keycloak authentication.

Affected Products

• Red Hat Keycloak (all versions prior to patch)
• Red Hat Single Sign-On 7.0

Discovery Timeline

• 2023-01-13 - CVE-2023-0105 published to NVD
• 2025-04-09 - Last updated in NVD database

Technical Details for CVE-2023-0105

Vulnerability Analysis

This vulnerability stems from improper authentication handling (CWE-287) in Keycloak's email trust mechanism. The flaw occurs when Keycloak fails to properly validate email address uniqueness and trust relationships between user accounts. When multiple accounts can be associated with the same email address without proper verification controls, an attacker can create a "shadow" account that mirrors a legitimate user's email identity.

The exploitation scenario allows an attacker to register or modify their account to use an email address already associated with another user. Because Keycloak does not properly enforce email trust boundaries, the attacker's account can interfere with the legitimate user's authentication flows, password reset mechanisms, and session management.

Root Cause

The root cause lies in Keycloak's insufficient validation of email address ownership and trust during user registration and account management operations. The system fails to enforce proper uniqueness constraints on email addresses across the user database, and does not implement adequate verification mechanisms to ensure email addresses are truly owned by the registering user before establishing trust relationships.

Attack Vector

The attack is network-accessible and requires no authentication or user interaction. An attacker can exploit this vulnerability by:

1. Identifying a target user's email address through reconnaissance
2. Registering a new account or modifying an existing account to use the target's email address
3. Leveraging the shared email identity to intercept password reset tokens, hijack sessions, or trigger account lockout policies against the legitimate user

The vulnerability enables both impersonation attacks (gaining unauthorized access as the victim) and denial-of-service attacks (locking legitimate users out of their accounts through failed authentication attempts on the shadow account).

Detection Methods for CVE-2023-0105

Indicators of Compromise

• Multiple user accounts registered with identical email addresses in Keycloak user database
• Unusual password reset requests for accounts with duplicate email configurations
• Authentication failures followed by successful logins from different user accounts sharing the same email
• User complaints about unexpected account lockouts or password reset notifications they did not initiate

Detection Strategies

• Implement database queries to identify duplicate email addresses across user accounts in the Keycloak realm
• Monitor authentication logs for patterns indicating email-based identity confusion between accounts
• Set up alerts for rapid succession of password reset requests targeting the same email address
• Review user provisioning logs for suspicious account creation patterns

Monitoring Recommendations

• Enable comprehensive audit logging for all Keycloak user registration and account modification events
• Monitor for anomalous patterns in email-based authentication flows and password recovery processes
• Implement real-time alerting on account lockout events to identify potential active exploitation
• Regularly audit the Keycloak user database for email address integrity violations

How to Mitigate CVE-2023-0105

Immediate Actions Required

• Review and apply the latest security patches from Red Hat for Keycloak and Single Sign-On products
• Audit existing user databases for duplicate email addresses and resolve conflicts
• Enable email verification requirements for all user registration and email change operations
• Consider implementing additional identity verification controls during authentication

Patch Information

Red Hat has acknowledged this vulnerability and provides security guidance through their advisory portal. Administrators should consult the Red Hat CVE-2023-0105 Advisory for specific patch versions and update instructions applicable to their deployment.

Workarounds

• Enforce unique email constraints at the database level to prevent duplicate email registrations
• Implement mandatory email verification workflows before establishing email trust relationships
• Configure account lockout policies with appropriate thresholds and administrator alerts
• Consider implementing additional authentication factors to reduce reliance on email-based identity

# Keycloak realm configuration - enforce email verification
# Access Keycloak Admin Console and navigate to:
# Realm Settings > Login > Verify Email = ON

# For CLI-based configuration using kcadm.sh:
./kcadm.sh update realms/your-realm -s verifyEmail=true
./kcadm.sh update realms/your-realm -s loginWithEmailAllowed=false
./kcadm.sh update realms/your-realm -s duplicateEmailsAllowed=false