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CVE-2026-56666 medium CVSS 4.8

Authentication Bypass in github.com/zitadel/zitadel (CVE-2026-56666)

Summary

Authentication bypass in github.com/zitadel/zitadel (CVE-2026-56666). Risk of unauthorized operations or information disclosure. Exploitable via AUTO_LINKING_OPTION_UNSPECIFIED. Mitigation: upgrade to 4.15.3 or later.

Original description

The description as published by the source.

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 automatica…

Source: NIST National Vulnerability Database NVD GitHub Advisory

Auto-generated summary

Assembled by SecPulse from the source data (CVSS, CWE, affected versions) using templates — no AI involved. Check the original description and references below for exact details.

A vulnerability tracked as CVE-2026-56666 has been found in github.com/zitadel/zitadel.
Attackers can target a specific entry point like AUTO_LINKING_OPTION_UNSPECIFIED over the network to misuse the product.
Risk of unauthorized operations or information disclosure. CVSS score: 4.8/10.
What to do: upgrade github.com/zitadel/zitadel to 4.15.3 or later.
If unsure, ask your IT team or search "github.com/zitadel/zitadel CVE-2026-56666" on the vendor's site.

CVE-2026-56666 (github.com/zitadel/zitadel) — CWE-287 / CVSS v3 4.8
Attack vector: remote (network-reachable) / unauthenticated / no user interaction
Attack surface: AUTO_LINKING_OPTION_UNSPECIFIED
Patched: 4.15.3 — apply immediately
Plan: 1) Audit SBOM/dependencies, 2) Stage→prod upgrade, 3) Add WAF/proxy monitoring on affected endpoints, 4) Hunt IOCs in logs.
Refs: see the GHSA / vendor advisory / patched release linked on this page.

❓ What is the problem

Authentication bypass (CWE-287) exists in github.com/zitadel/zitadel. Attackers reach the vulnerable code path via AUTO_LINKING_OPTION_UNSPECIFIED without authentication.

📍 Affected scope

Check the vendor advisory for the affected versions of github.com/zitadel/zitadel. Attack surface: AUTO_LINKING_OPTION_UNSPECIFIED.

🔥 Severity

Severity: Medium (CVSS 4.8/10). Risk of unauthorized operations or information disclosure.

🔧 How to fix

Update to 4.15.3.

🛡️ Workaround

Until the patch is applied: disable the affected feature, apply WAF rules, or restrict access via network ACLs.

🔍 Detection

Search webserver/proxy logs for unusual request patterns matching this CVE's known IOCs. Run grep -r 'github.com/zitadel/zitadel' . against your dependency files (package-lock.json, requirements.txt, go.sum) to find affected services.

Response actions

Concrete steps and command examples for SOC/SRE teams to execute in order

  1. 1
    Identify exposure identify 
    grep -r 'github.com/zitadel/zitadel' . | grep -v node_modules

    リポジトリと本番環境の依存ファイル (package-lock.json / requirements.txt / go.sum / Gemfile.lock 等) で github.com/zitadel/zitadel を grep し、稼働しているサービス・バージョンを把握する。

  2. 2
    Apply patch patch 
    Upgrade github.com/zitadel/zitadel to 4.15.3

    ステージング環境で 4.15.3 に上げて回帰テスト → 本番反映。回帰テストはアプリの主要ハッピーパスを含めること。

  3. 3
    Post-deployment verification verify 
    Confirm patched version is live in production

    パッチ適用後、ステージングで PoC または同等の悪用パターンを再現して脆弱性が閉じたことを確認。本番ではアクセスログ・WAF でアラート再発が無いか継続監視。

Affected packages

go github.com/zitadel/zitadel
[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"4.15.3"}]}]

References

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