CVE-2026-84458: Zammad: Account takeover via unverified email matching during SSO auto-link
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 xmsedov 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.
Affected Software
Remediation
Recommended actions to resolve this vulnerability, in priority order.
- Upgrade
Upgrade
Zammadto a version that resolves this vulnerability.Fixed in 7.1.2
Event History
Frequently Asked Questions
Which deployments are exposed to this issue?
Deployments running a version prior to 7.1.2 are affected when "Automatic account link on initial logon" is enabled. The issue can affect any existing local account, including agent and administrator accounts.
What does an attacker need to exploit it?
An attacker needs control of an identity at a configured third-party SSO provider and must be able to set that identity's email address to the target account's address. For the default multi-tenant Microsoft 365 /common app registration, this can include an identity from any Azure AD tenant.
Does the victim need to disclose their local password?
No. Successful exploitation bypasses the victim's local password because the incoming SSO identity is automatically linked to the existing account based on its reported email address.
How does Microsoft 365 email verification affect exposure?
When email verification is required in the Microsoft 365 setting, Zammad honors the xms_edov ID token claim. A missing claim is treated as an unverified email.
What version fixes the issue?
The issue is fixed in Zammad version 7.1.2.