ZITADEL: Missing authentication allows username change in Login V1
Summary
The hosted Login V1 UI of ZITADEL changes a username before the login flow has verified any authentication factor. An unauthenticated attacker who knows a victim's login name can rename any active human user, including instance administrators, which locks the legitimate owner out. The attacker cannot take over the account, because no password, session or token is disclosed.
Affected
- ZITADEL 4.0.0 to 4.17.3 (including RC versions)
- ZITADEL 3.0.0 to 3.4.15 (including RC versions)
- Only deployments that use the hosted Login V1 UI. Login V2 is not affected through this flow. Machine and service accounts are not affected.
Fixed in
- ZITADEL 4.x: upgrade to v4.19.1 or later. Skip v4.18.0, because the setup step fails in that version.
- ZITADEL 3.x: no fix will be provided. The 3.x line reached end of life on 2026-08-31, so upgrade to a patched 4.x release.
- The CVE record lists 4.18.0 as unaffected, but the vendor advisory recommends v4.19.1.
Workaround
- No configuration fully closes the gap on unpatched versions. Upgrading is the only complete fix.
- Until the upgrade is done, restrict network access to the Login V1 UI, for example with a reverse proxy allowlist.
Exploitation
- CISA SSVC: exploitation none, automatable yes, technical impact partial.
- No evidence of exploitation in the wild was found. The CVE is not listed in CISA KEV.
- No public proof of concept was found in our research. This is not confirmed absent.
Our recommendation
- Identify all ZITADEL instances and their versions. Prioritize internet-exposed instances that run Login V1.
- Upgrade 4.x instances to v4.19.1 or later, and migrate 3.x instances to a patched 4.x release.
- Until then, limit access to the Login V1 UI and review audit logs for unexpected username changes, especially for administrator accounts.
- Make sure administrator access can be recovered if an account is renamed.
Public exploits
PoC-in-GitHub, Metasploit and Exploit-DB list nothing for this CVE.
Research sources
- GitHub Security Advisory GHSA-4hgj-wm6c-q7p2 github.com
- VulnCheck advisory for CVE-2026-109371 www.vulncheck.com
- OpenCVE record CVE-2026-109371 app.opencve.io
- ZITADEL hosted login documentation zitadel.com
- VulDB entry 417150 vuldb.com
Researched and written up in English and German by an AI (Claude by Anthropic) based on NVD, CISA, EPSS and the sources listed. The vendor information is authoritative. Researched on 31 Oct 2026, 20:26.
Original description (NVD)
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.
Sources
The tracker combines official, freely usable data sources – updated continuously:
- NVD (NIST) – CVEs, rating (CVSS), affected products
- CISA KEV – vulnerabilities confirmed by CISA as actively exploited
- CISA Vulnrichment – CISA assessment (SSVC) in the official CVE record
- FIRST EPSS – probability of exploitation
- Microsoft MSRC – Patch Tuesday: vulnerabilities, severity, updates
- PoC-in-GitHub – public proof-of-concept repositories
- Metasploit (Rapid7) – modules of the Metasploit Framework
- Exploit-DB (OffSec) – archive of public exploits (links only)
- Patch days: official vendor pages (linked per vendor) (Vendor patch days)
This product uses data from the NVD API but is not endorsed or certified by the NVD. EPSS data © FIRST.org.
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