CVE-2026-40872
Official description Straight from the sourceThe vendor's or NVD's own wording, published unedited. Authoritative, but often terse — it says what broke, rarely what to do.
NVD · uneditedmailcow: dockerized is an open source groupware/email suite based on docker. In versions prior to 2026-03b, the admin dashboard's Autodiscover logs render the EMailAddress value (logged as the "user" field) without HTML escaping. By submitting an unauthenticated Autodiscover request with a crafted EMailAddress containing HTML/JS, the payload is stored in Redis and executed when an admin views the Autodiscover logs. Version 2026-03b fixes the vulnerability.
Technical summary Written by usOur analysis, written from the advisory, the CVSS vector and the affected-version data. It adds context the advisory leaves out, and never invents facts that are not in the source.
dbcve analysis · high confidencemailcow: dockerized versions prior to 2026-03b contain a stored XSS vulnerability in the admin dashboard's Autodiscover logs. The EMailAddress parameter from unauthenticated Autodiscover requests is logged to Redis without HTML escaping and executes in the admin's browser when viewing the logs.
Verify against the referenced sources before acting — the references below are authoritative for this CVE, this summary is not.
CVSS breakdown How the score is builtThe industry scoring standard. It rates how the flaw is reached, what it takes to exploit, and what an attacker gains — the score is derived from those, not the other way round.
From the vector- Attack vector
- Network
- Complexity
- Low
- Privileges
- None
- Authentication
- X
- User interaction
- P
- Scope
- X
CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:P/VC:H/VI:H/VA:H/SC:H/SI:H/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X
Am I affected? How to checkSteps we derive from the advisory and the affected-version data, so you can decide whether this CVE reaches your setup. They are a guide, not a scan — your own configuration is the authority.
dbcve checksWork through these to decide whether this CVE applies to you.
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Determine installed mailcow versionCheck the mailcow version by viewing the mailcow.conf file or running: docker ps --format '{{.Image}}' | grep mailcow or checking the VERSION file in the mailcow directoryAffected if The installed version is prior to 2026-03b (e.g., 2026-03a, 2026-02x, etc.)
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Check if Autodiscover service is enabledInspect the mailcow.conf file for Autodiscover-related settings or check if the autodiscover-service container is running via: docker ps | grep autodiscoverAffected if Autodiscover is enabled and the service is active in the environment
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Identify if admin dashboard logs are accessibleLog into the mailcow admin web interface and navigate to the Autodiscover logs section (typically under Logs or Debug) to confirm the endpoint is accessibleAffected if You have administrative access to view Autodiscover logs in the admin dashboard
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Verify Redis logging behavior for AutodiscoverCheck Redis for stored Autodiscover entries: docker exec -it $(docker ps -qf name=redis-mailcow) redis-cli KEYS '*autodiscover*' and inspect stored EMailAddress valuesAffected if Autodiscover requests are being logged to Redis and the EMailAddress field contains raw, unescaped input
You are affected if running any mailcow: dockerized version prior to 2026-03b with Autodiscover enabled and admin access to view the Autodiscover logs in the dashboard.
Generated from the published advisory. Verify against your own configuration.
Remediation Closing itWhat it takes to close this. Where a vendor fix exists we point at it; where none exists we say so plainly, and can build one. Effort estimates are scoped from the advisory, not from your codebase.
dbcve · scopedUpgrade mailcow to version 2026-03b or later which applies proper HTML escaping to the EMailAddress field in Autodiscover logs.
2026-03b
- Upgrade mailcow to version 2026-03b or later to obtain the fix for the XSS vulnerability
- After upgrading, verify that the Autodiscover logs now properly HTML-escape the EMailAddress/user field before rendering
- Confirm the fix by logging into the admin dashboard and reviewing the Autodiscover logs section
Generated from the published advisory — verify against the referenced sources before acting.
- Consultation2.0 h
- Implementation2.0 h
- Testing2.0 h
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Scan for this in your stack
Free · runs locallyCheck whether your project pulls in CVE-2026-40872 — or any other known-vulnerable package — straight from your lock files. Free and open source; it runs locally and uploads nothing.
References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.
Primary sourcesPractitioner notes
ContributedPeer-ranked notes from engineers who’ve handled CVE-2026-40872 in production — separate from our analysis above.
The advisory tells you what broke. It rarely tells you what actually worked. If you’ve dealt with this one, that detail is what the next engineer is searching for.
- The version that genuinely resolved it — not the one the vendor claimed
- A config change or rule that shut the vector down
- A gotcha in the upgrade path that cost you an afternoon
No notes yet
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- Verified mitigations, workarounds, and config changes
- Version or environment caveats, and links to real fixes
- No weaponised exploit code, or anything meant to cause harm
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