CVE-2026-23511: ZITADEL has a user enumeration vulnerability in Login UIs
Summary
A user enumeration vulnerability has been discovered in Zitadel's login interfaces. An unauthenticated attacker can exploit this flaw to confirm the existence of valid user accounts by iterating through usernames and userIDs.
Impact
The login UIs (in version 1 and 2) provide the possibility to request a password reset, where an email will be sent to the user with a link to a verification endpoint. By submitting arbitrary userIDs to these endpoints, an attacker can differentiate between valid and invalid accounts based on the system's response.
For an effective exploit the attacker needs to iterate through the potential set of userIDs. The impact can be limited by implementing rate limiting or similar measures to limit enumeration of userIDs.
Additionally, Zitadel includes a security feature "Ignoring unknown usernames", designed to prevent username enumeration attacks by presenting a generic response for both valid and invalid usernames on the login page. The login UI V2 did not handle the setting correctly and would allow attackers to enumerate through usernames to check their existence.
Affected Versions
All versions within the following ranges, including release candidates (RCs), are affected: - v4.x: 4.0.0 through 4.9.0 - 3.x: 3.0.0 through 3.4.5 - 2.x: 2.0.0 through 2.71.19
Patches
The vulnerability has been addressed in the latest releases. The patch resolves the issue by returning a generic error message, which does not indicate it the user exists.
4.x: Upgrade to >=4.9.1 3.x: Update to >=3.4.6 2.x: Update to >=3.4.6
Workarounds
The recommended solution is to update ZITADEL to a patched version. You can limit the impact by implementing rate limiting or similar measures to limit enumeration of userIDs.
There is no workaround for the "Ignoring unknown usernames" issue in login V2. Please upgrade to a patched version, if you rely on this feature.
Questions
If you have any questions or comments about this advisory, please email us at security@zitadel.com
Credits
Thanks to Niklas Kunz from Seamly for reporting this vulnerability from their pentest.
Other sources
ZITADEL is an open source identity management platform. Prior to 4.9.1 and 3.4.6, a user enumeration vulnerability has been discovered in Zitadel's login interfaces. An unauthenticated attacker can exploit this flaw to confirm the existence of valid user accounts by iterating through usernames and userIDs. This vulnerability is fixed in 4.9.1 and 3.4.6.
— MITRE
Affected Software
Remediation
Event History
Frequently Asked Questions
What is the severity of CVE-2026-23511?
CVE-2026-23511 is classified as a user enumeration vulnerability that can lead to exposure of valid user accounts.
How do I fix CVE-2026-23511?
To fix CVE-2026-23511, upgrade Zitadel to version 3.4.6 or 4.9.1, which address this vulnerability.
What impact does CVE-2026-23511 have on security?
The impact of CVE-2026-23511 allows attackers to confirm the existence of user accounts, increasing the risk of targeted attacks.
What versions of Zitadel are affected by CVE-2026-23511?
Zitadel versions up to and including 3.4.5 and 4.0.0 up to 4.9.0 are affected by CVE-2026-23511.
Is authentication required to exploit CVE-2026-23511?
No, CVE-2026-23511 can be exploited by an unauthenticated attacker.