CVE-2026-86009: Mailu: Domain managers can allow themselves to spoof on other hosted domains they should not control
Mailu is a mail server distributed as a set of Docker images. Prior to f05aeb8322e2f61096af6b089d61ba6f40587d96, domain managers can enable spoofing for hosted domains they do not control. A potentially malicious domain administrator enables spoofing for another hosted domain and can send emails that are authenticated with DKIM/SPF for domains they should not be able to. This vulnerability is addressed by f05aeb8322e2f61096af6b089d61ba6f40587d96.
Affected Software
Remediation
Recommended actions to resolve this vulnerability, in priority order.
- Upgrade
Upgrade
Mailuto a version that resolves this vulnerability.Patch f05aeb8322e2f61096af6b089d61ba6f40587d96
Event History
Frequently Asked Questions
Who can exploit this issue?
A domain manager or administrator with access to Mailu's domain-management functionality can exploit it. The attacker must be able to enable spoofing for another hosted domain.
What is the impact of successful exploitation?
The attacker can send messages impersonating another hosted domain that they do not control. Those messages can be authenticated with DKIM and SPF for the impersonated domain.
Are all Mailu deployments affected?
Deployments using a revision prior to f05aeb8322e2f61096af6b089d61ba6f40587d96 are affected when domain managers can manage spoofing settings. The issue is fixed in revision f05aeb8322e2f61096af6b089d61ba6f40587d96.