CVE-2026-84458 Zammad: Account takeover via unverified email matching during SSO auto-link

What is CVE-2026-84458?

CVE-2026-84458 is a critical authentication bypass vulnerability in zammad, published on 25 Sep 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.

Official description

Zammad is a web based open source helpdesk/customer support system. Prior to 7.1.2, when the "Automatic account link on initial logon" setting is enabled, Zammad binds an incoming third-party (SSO) identity to an existing local account by matching the email address the identity provider reports, without verifying that the provider actually confirmed ownership of that email. An attacker who controls any identity at a configured provider, including, by default, any Azure AD tenant via Zammad's multi-tenant Microsoft 365 /common app registration, can set that identity's email to a victim's address, authenticate, and be logged in as the victim. This bypasses the victim's local password entirely and affects any existing account, including agents and administrators. Zammad will honor the xms_edov ID token claim when email verification is required in the Microsoft 365 setting, treating a missing claim as unverified. This issue is fixed in version 7.1.2.

Weakness: CWE-287

Which versions are affected by CVE-2026-84458?

How do I fix CVE-2026-84458?

No fix has been published for CVE-2026-84458 yet. Limit exposure of the affected software until one is available.

Upgrade, and rotate credentials and sessions that may have been exposed. More about Authentication bypass.

Is CVE-2026-84458 being exploited?

There is no known exploitation of CVE-2026-84458 in the wild and no public exploit code.

Sources

• CVE record
• NVD
• OSV
• GitHub advisory
• How this page is made

Also known as GHSA-86cc-3ggh-mf2m.