CVE-2021-3754 in Keycloak
Summary
by MITRE • 08/26/2022
A flaw was found in keycloak where an attacker is able to register himself with the username same as the email ID of any existing user. This may cause trouble in getting password recovery email in case the user forgets the password.
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Analysis
by VulDB Data Team • 10/02/2022
The vulnerability identified as CVE-2021-3754 represents a critical username collision issue within the Keycloak identity and access management platform. This flaw exists in the user registration process where the system fails to properly validate username uniqueness when it matches an existing user's email address. The technical implementation allows malicious actors to exploit this weakness by registering with a username that exactly matches another user's email identifier, creating a dangerous scenario where legitimate users may lose access to their account recovery mechanisms.
This vulnerability stems from inadequate input validation and user account management controls within Keycloak's authentication framework. The flaw specifically manifests when the system permits duplicate username entries without proper enforcement of uniqueness constraints, particularly when usernames are allowed to match email addresses of existing accounts. The underlying issue can be categorized under CWE-257 as it involves insecure storage of credentials and user account information, while also demonstrating characteristics of CWE-306 as it presents an authentication bypass opportunity through account takeover.
The operational impact of this vulnerability extends beyond simple account confusion, creating significant security risks for organizations relying on Keycloak for identity management. When an attacker successfully registers with a username matching an existing user's email, legitimate users face potential account lockout scenarios and loss of password recovery functionality. This creates a denial of service condition where users cannot access their accounts through normal recovery mechanisms, potentially leading to extended service disruption and requiring manual administrative intervention to resolve. The vulnerability also opens pathways for social engineering attacks where attackers can target specific users by leveraging their email addresses to gain unauthorized access to accounts.
Organizations utilizing Keycloak should implement immediate mitigations including enhanced username validation rules that prevent registration of usernames matching existing email addresses, along with comprehensive monitoring of user registration activities for suspicious patterns. The system should enforce strict uniqueness constraints across both username and email fields, ensuring that no user can register with credentials that would conflict with existing accounts. Additionally, administrators should consider implementing rate limiting on registration attempts and regular audits of user accounts to identify and remediate any existing conflicts. This vulnerability aligns with attack patterns documented in the MITRE ATT&CK framework under T1078 for valid accounts and T1531 for account access removal, emphasizing the importance of proper identity management controls and the potential for privilege escalation through account takeover techniques.