CVE-2026-23511

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.

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

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 [email protected]

Credits

Thanks to Niklas Kunz from Seamly for reporting this vulnerability from their pentest.

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.

CVE-2026-23511 has a CVSS score of 5.3 (Medium). The vector is network-reachable, no privileges required, and no user interaction. A CVSS score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether this affects your application depends on whether the vulnerable code is present and reachable in your environment. A fixed version is available (4.9.1, 3.4.6); upgrading removes the vulnerable code path.

Kodem intelligence

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

1. What is CVE-2026-23511? CVE-2026-23511 is a medium-severity security vulnerability in github.com/zitadel/zitadel (go), affecting versions >= 4.0.0, <= 4.9.0. It is fixed in 4.9.1, 3.4.6.
2. How severe is CVE-2026-23511? CVE-2026-23511 has a CVSS score of 5.3 (Medium). This score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether it represents real risk in your environment depends on whether the vulnerable code is present and reachable.
3. Which versions of github.com/zitadel/zitadel are affected by CVE-2026-23511? github.com/zitadel/zitadel (go) versions >= 4.0.0, <= 4.9.0 is affected.
4. Is there a fix for CVE-2026-23511? Yes. CVE-2026-23511 is fixed in 4.9.1, 3.4.6. Upgrade to this version or later.
5. Is CVE-2026-23511 exploitable, and should I be worried? Whether CVE-2026-23511 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
6. What actually determines whether CVE-2026-23511 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
7. How do I fix CVE-2026-23511?
   • Upgrade github.com/zitadel/zitadel to 4.9.1 or later
   • Upgrade github.com/zitadel/zitadel to 3.4.6 or later