VulnerabilityPublished 11 Sep 2026

CVE-2026-56666: Auto-linking by email · IdP-side email verification is not checked

Affects github.com/zitadel/zitadelSource GCVE Database

Not known to be exploited · CVSS 4.8 Medium : upgrade to 4.15.3 when convenient.

Data as of 27 Oct 2026, 05:11 UTC

CVSS 3.1 base score

4.8Medium

How severe the flaw is on the 0–10 CVSS scale.

EPSS: 0.2% chance of exploitation in 30 days – higher than 20% of CVEsExploit Prediction Scoring System: the likelihood attackers will use this flaw soon.
Patch: Available – fixed in 4.15.3

CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:L/A:N

Attack Vector: Network
Attack Complexity: High
Privileges Required: None
User Interaction: None
Scope: Unchanged
Confidentiality: Low
Integrity: Low
Availability: None

Bold values are the worst case: easiest to exploit or largest impact.

Attack Vector: Network: The vulnerable component is bound to the network stack and the set of possible attackers extends beyond the other options listed, up to and including the entire Internet. Such a vulnerability is often termed 'remotely exploitable' and can be thought of as an attack being exploitable at the protocol level one or more network hops away (e.g., across one or more routers).
Attack Complexity: High: A successful attack depends on conditions beyond the attacker's control. That is, a successful attack cannot be accomplished at will, but requires the attacker to invest in some measurable amount of effort in preparation or execution against the vulnerable component before a successful attack can be expected. For example, a successful attack may require an attacker to: gather knowledge about the environment in which the vulnerable target/component exists; prepare the target environment to improve exploit reliability; or inject themselves into the logical network path between the target and the resource requested by the victim in order to read and/or modify network communications (e.g., a man in the middle attack).
Privileges Required: None: The attacker is unauthorized prior to attack, and therefore does not require any access to settings or files to carry out an attack.
User Interaction: None: The vulnerable system can be exploited without any interaction from any user.
Scope: Unchanged: An exploited vulnerability can only affect resources managed by the same security authority. In this case, the vulnerable component and the impacted component are either the same, or both are managed by the same security authority.
Confidentiality: Low: There is some loss of confidentiality. Access to some restricted information is obtained, but the attacker does not have control over what information is obtained, or the amount or kind of loss is limited. The information disclosure does not cause a direct, serious loss to the impacted component.
Integrity: Low: Modification of data is possible, but the attacker does not have control over the consequence of a modification, or the amount of modification is limited. The data modification does not have a direct, serious impact on the impacted component.
Availability: None: There is no impact to availability within the impacted component.

Definitions: FIRST CVSS v3.1 specification.

Exploitation evidence

Disclosed: evidence found.
CVE published 11 Sep 2026
Detectable: no evidence on record.
No public nuclei template indexed
Weaponised: no evidence on record.
No public exploit code indexed in Metasploit or Exploit-DB
Exploited in the wildExploited: no evidence on record.
Not in CISA KEV and no source reports exploitation
Observed by OffSeq MirageSeen by Mirage: no evidence on record.
No attack traffic recorded by OffSeq Mirage sensors

A missing step is not evidence of safety. Sources: cve.org (opens in a new tab), the Metasploit, Exploit-DB and nuclei-templates index as of 26 Oct 2026.

Disclosed: The CVE record is public on cve.org. Its publication is t = 0.
Detectable: A public nuclei template can find exposed instances, for defenders and attackers alike.
Weaponised: Public exploit code exists in Metasploit or Exploit-DB, or CISA SSVC or the CVSS exploit maturity reports a public proof of concept.
Exploited in the wild: CISA KEV lists it, CISA SSVC rates exploitation active, or a source reports attacks.
Observed by OffSeq Mirage: OffSeq Mirage honeypot sensors recorded attack traffic for this CVE, or found exposed hosts without attack traffic.

Moments are spaced evenly, not to scale; a dashed line marks a gap of six months or more. Deltas count from t = 0. Sources that give only a date (CISA KEV, Exploit-DB, or a time of exactly 00:00Z) read “same day” rather than hours. Metasploit modules carry the flaw’s disclosure date, not their release date, and nuclei templates carry no date, so both appear above but not on the timeline.

What to do

Upgrade github.com/zitadel/zitadel to 4.15.3.

Affected software

Product	Affected	Fixed in
Gogithub.com/zitadel/zitadel	Affected <4.15.3	Fixed in 4.15.3

Check your own hosts for these packages with threat-finder (opens in a new tab), our free open-source scanner.

AI-suggested

A patch is available in ZITADEL version 4.15.3 and later that enforces verification of the external identity provider's email verification status before auto-linking accounts. Administrators should upgrade to these versions to remediate the vulnerability. If immediate upgrade is not possible, disable auto-linking by email on affected identity providers or restrict auto-linking to trusted enterprise identity providers that enforce strict email verification policies.

Description

### Summary A flaw in the external identity provider handler allows unauthorized account linking to occur under specific administrative configurations. When auto-linking by email is enabled, ZITADEL checks that the local user's email is verified, but does not explicitly cross-check whether the incoming external identity provider (IdP) also verified that email address upstream. ### Impact When a user logs in via an external identity provider, the system can automatically link them to an existing local account if their email addresses match. However, because the system fails to check if the external provider actually verified ownership of that email, a security risk is introduced if a loose or public provider is connected. If an administrator enables email auto-linking for an external identity provider that allows anyone to sign up with an unverified email address, an attacker can exploit this behavior. By registering an account on that permissive provider using a victim's email address and logging in, the system will automatically link the attacker's federated identity to the victim's legitimate local account. This allows the attacker to log into the victim's account without requiring any interaction or confirmation from the victim. This issue represents a configuration-dependent anomaly rather than an unconditioned attack vector. Because the scenario relies entirely on an explicit administrative choice to trust a permissive external directory and link accounts automatically based purely on email strings, the practical operational risk is classified as **Medium**. ### Affected Versions Systems running one of the following versions are affected: * **4.x:** `4.0.0` through `4.15.2` (including RC versions) * **3.x:** `3.0.0` through `3.4.12` (including RC versions) ### Patches The vulnerability has been addressed in the latest releases. The patch resolves the issue by requiring that the external identity provider's email verification status is explicitly validated before allowing any automatic linking logic to proceed. * **4.x**: Upgrade to $\ge$ [4.15.3](https://github.com/zitadel/zitadel/releases/tag/v4.15.3) * **3.x**: Upgrade to $\ge$ [4.15.3](https://github.com/zitadel/zitadel/releases/tag/v4.15.3) ### Workarounds If an immediate upgrade is not possible, implement one of the following mitigations: * Disable auto-linking by email entirely by setting the option to `AUTO_LINKING_OPTION_UNSPECIFIED` on corresponding identity providers. * Audit external IdP configurations and restrict email auto-linking strictly to trusted enterprise identity directories (e.g., corporate Okta or Azure AD) where email verification is strictly enforced and managed by corporate policy. ### Questions If you have any questions or comments about this advisory, please email us at [security@zitadel.com](mailto:security@zitadel.com) ### Credits Thanks to [Android-Login-Analysis](https://github.com/Android-Login-Analysis) and [Alejandro Yadlin](https://github.com/ayadlin) for reporting this vulnerability.

Impact

The vulnerability allows an attacker to gain unauthorized access to a victim's local account by exploiting the automatic email-based account linking feature when used with an external identity provider that does not enforce email verification. This can lead to account compromise without victim interaction. However, the risk is medium and depends on the administrator enabling auto-linking with a permissive external IdP.

Summary

The vulnerability in ZITADEL (CVE-2026-56666) arises from insufficient verification of email ownership from external identity providers during automatic account linking by email. While the local user's email verification is checked, the system does not confirm that the external IdP has verified the email address. If an administrator enables auto-linking with an external IdP that allows unverified email signups, an attacker can register using a victim's email and gain unauthorized access by linking to the victim's local account. This flaw is configuration-dependent and affects ZITADEL versions 3.0.0 through 3.4.12 and 4.0.0 through 4.15.2. The issue is fixed in version 4.15.3 and later by requiring explicit validation of the external IdP's email verification status before linking.

CWE-287Improper Authentication (opens in a new tab)
Class weaknessLikelihood of exploit: HighOWASP Top 10 A07:2025: Authentication Failures (opens in a new tab)
When an actor claims to have a given identity, the product does not prove or insufficiently proves that the claim is correct.
MITRE discourages mapping vulnerabilities to this broad entry; the root cause is usually a more specific weakness.
Architecture and Design · Libraries or Frameworks
Use an authentication framework or library such as the OWASP ESAPI Authentication feature.
OWASP Cheat Sheets
OWASP Authentication (opens in a new tab)
OWASP ASVS 4.0.3
V2.8.5 (opens in a new tab)
V2.8.4 (opens in a new tab)
V9.2.3 (opens in a new tab)
Attack patterns
Fake the Source of Data (opens in a new tab)
Utilizing REST's Trust in the System Resource to Obtain Sensitive Data (opens in a new tab)
Session Hijacking (opens in a new tab)
Token Impersonation (opens in a new tab)
Upload a Web Shell to a Web Server (opens in a new tab)
From MITRE CWE, MITRE CAPEC and OWASP (Top 10, OpenCRE).

References

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Exploitation evidence

What to do

Affected software

Description

AI analysisMachine-generated, updated 12 Sep 2026, 00:44 UTC

WeaknessesCWE-287

Technical details

References

Community reviews

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