CVE-2026-109371 in Zitadel
Summary
by MITRE • 10/12/2026
ZITADEL 3.0.0 before 4.18.0 contains a missing authentication vulnerability in the hosted Login V1 UI, where the change-username handler acts on the account bound to a login flow before any factor is verified. Unauthenticated attackers can submit a victim's login name and then post a new username to rename any active human user, including administrators, locking them out.
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Analysis
by VulDB Data Team • 10/12/2026
The vulnerability identified in ZITADEL versions prior to 4.18.0 represents a critical failure in the authentication workflow of its hosted Login V1 UI interface. Specifically, this flaw resides within the change-username handler, which processes requests to modify user account names without enforcing proper identity verification protocols. In a secure system architecture, any operation that alters sensitive account attributes such as usernames must be preceded by robust multi-factor authentication or at least strong session validation to ensure the requester is indeed the legitimate owner of the account. However, in this affected version, the handler acts on the account bound to an active login flow before any security factor has been successfully verified. This architectural oversight creates a significant gap where unauthenticated actors can interact with user management functions under the guise of a standard authentication attempt that has not yet completed its verification steps.
From a technical perspective, this flaw allows for unauthorized modification of user identities by leveraging the state of an active login session. An attacker who gains access to or observes a victim's login name during the initial stages of authentication can exploit this window of opportunity. By submitting the victim's identifier and subsequently posting a request with a new username, the system processes these changes without confirming that the person making the change is authorized to do so. This mechanism effectively bypasses the intended security controls designed to protect account integrity. The vulnerability is particularly severe because it affects all human users within the system, including those with administrative privileges. Since administrators often hold elevated permissions and access critical infrastructure data, compromising their accounts can lead to widespread systemic compromise rather than just individual user impact.
The operational impact of this missing authentication flaw is substantial, primarily centering on account takeover and denial of service through identity manipulation. By successfully renaming an active human user, including high-privilege administrators, the attacker effectively locks the legitimate owner out of their own account. This action disrupts business continuity for individuals relying on these accounts for daily operations and can halt critical administrative tasks if a system administrator is targeted. Furthermore, this capability facilitates unauthorized access to data associated with the victim's identity. Once the username is changed, the original user may lose access to resources tied to that specific identifier, while the attacker gains control over the account under its new name. This type of attack undermines trust in the authentication provider and can lead to significant reputational damage for organizations relying on ZITADEL for their identity management needs.
This vulnerability aligns with CWE-287, which describes Improper Authentication, as well as CWE-640, Weak Password Recovery Mechanisms for Forgotten Passwords if the rename process is used in conjunction with password reset flows to hijack accounts. In terms of offensive security frameworks, this behavior corresponds to MITRE ATT&CK technique T1098, specifically SSH Account Manipulation or general Account Modification techniques where an adversary alters account properties to maintain access or disrupt services. The exploitation path involves manipulating the authentication state machine, which is a common vector in modern identity and access management systems when session handling logic is not strictly enforced across all administrative endpoints.
To mitigate this vulnerability, organizations must immediately upgrade ZITADEL to version 4.18.0 or later, where these issues have been addressed by enforcing strict verification steps before allowing any changes to user attributes. Until the update can be applied, administrators should review their login flow configurations to ensure that no sensitive operations are exposed during unverified stages of authentication. Implementing additional monitoring for unusual username change requests and restricting access to administrative functions based on role-based access control principles can also help reduce the risk surface. Regular audits of identity management policies and ensuring that all endpoints adhere to zero-trust principles where every action is verified regardless of session state are essential practices for maintaining robust security posture in identity infrastructure.