# CVE-2026-86009: Mailu domain manager email spoofing authorization bypass

Source: https://junglewise.ai/threats/cve-2026-86009-mailu-is-a-mail-server-distributed-as-a-set-of-docker-images  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-10-16. Updated: 2026-10-16  
License: CC BY 4.0 with a link back

CVE-2026-86009 · Severity: info · Published 2026-10-16

Mailu is a mail server that allows administrators to manage hosted email domains. A domain manager can improperly enable email spoofing permissions for themselves or other users on domains they don't control, allowing them to send forged emails that appear to come from other domains' addresses with valid DKIM/SPF authentication. This could allow unauthorized parties to conduct phishing attacks or fraud using trusted domain identities.

Technologies: [Mailu](https://junglewise.ai/threats/technologies/mailu). Vendors: [Mailu](https://junglewise.ai/threats/vendors/mailu).

## Quick answers

**Is CVE-2026-86009 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-86009 being exploited in the wild.

**How severe is CVE-2026-86009?** Informational severity, published 16 October 2026.

**Which products and versions are affected?** Mailu prior to f05aeb8322e2f61096af6b089d61ba6f40587d96.

**Is there a fix for CVE-2026-86009?** Yes: fixed in f05aeb8322e2f61096af6b089d61ba6f40587d96 onwards. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

**How is CVE-2026-86009 attacked?** It is attacked over the network, in a hosted service.

**Am I affected by CVE-2026-86009?** Check whether you run Mailu at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

## How to fix

- Fixed in f05aeb8322e2f61096af6b089d61ba6f40587d96 onwards

## Technical details

The vulnerability is an authorization bypass in the allow_spoofing user field, which is controlled by domain managers through user creation/editing endpoints. The /postfix/sender/login lookup unioned all users with allow_spoofing=True regardless of domain scope, making it instance-wide send-as-anyone capability. A domain manager could grant themselves allow_spoofing and send authenticated emails on domains they do not manage. The fix (commit f05aeb8) scopes the lookup to the sender's own domain.

## Affected products

- Mailu Mailu prior to f05aeb8322e2f61096af6b089d61ba6f40587d96

## Timeline

- 2026-10-16: disclosed

## References

- [https://github.com/Mailu/Mailu/commit/f05aeb8322e2f61096af6b089d61ba6f40587d96](https://github.com/Mailu/Mailu/commit/f05aeb8322e2f61096af6b089d61ba6f40587d96)
- [https://github.com/Mailu/Mailu/issues/2686](https://github.com/Mailu/Mailu/issues/2686)

## Related threats

- [Mailu authorization bypass in admin account management](https://junglewise.ai/threats/cve-2026-86008-mailu-is-a-mail-server-distributed-as-a-set-of-docker-images)
- [Mailu mail server authentication bypass via header spoofing](https://junglewise.ai/threats/cve-2026-85751-mailu-is-a-mail-server-distributed-as-a-set-of-docker-images-from)
- [Mailu admin REST API missing authentication in token endpoint](https://junglewise.ai/threats/cve-2026-49217-mailu-admin-rest-api-missing-authentication-in-token-endpoint)