CVE-2026-40871
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. Versions prior to 2026-03b have a second-order SQL injection vulnerability in the quarantine_category field via the Mailcow API. The /api/v1/add/mailbox endpoint stores quarantine_category without validation or sanitization. This value is later used by quarantine_notify.py, which constructs SQL queries using unsafe % string formatting instead of parameterized queries. This results in a delayed (second-order) SQL injection when the quarantine notification job executes, allowing an attacker to inject arbitrary SQL. Using a UNION SELECT, sensitive data (e.g., admin credentials) can be exfiltrated and rendered inside quarantine notification emails. 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 confidenceA second-order SQL injection vulnerability exists in mailcow dockerized versions prior to 2026-03b. The /api/v1/add/mailbox endpoint accepts a quarantine_category value without validation, which gets stored directly. Later, when quarantine_notify.py executes, it uses unsafe % string formatting to incorporate this stored value into SQL queries rather than parameterized queries. An authenticated attacker can inject arbitrary SQL payloads that execute during the quarantine notification job, potentially exfiltrating sensitive data like admin credentials through notification emails.
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
- High
- User interaction
- None
- Scope
- Unchanged
- Confidentiality
- High
- Integrity
- High
- Availability
- High
CVSS:3.1/AV:N/AC:L/PR:H/UI:N/S:U/C:H/I:H/A:H
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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Identify mailcow installation location and versionCheck for the mailcow-dockerized directory, typically at /opt/mailcow-dockerized, and look for a version file or check the docker-compose.yml image tags for the installed versionAffected if The installed version is prior to 2026-03b (e.g., 2026-03a, 2025-xx, etc.)
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Locate the vulnerable API endpoint definitionSearch the mailcow source for the /api/v1/add/mailbox endpoint handler and inspect how the quarantine_category parameter is processed before storageAffected if The quarantine_category parameter is accepted without input validation or sanitization before being stored
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Examine quarantine_notify.py for SQL construction patternsFind the quarantine_notify.py file in the mailcow installation and inspect the SQL query construction. Look for uses of % string formatting (e.g., cursor.execute('SELECT ... WHERE %s', value) or similar patterns) rather than parameterized queriesAffected if The file uses % string formatting or .format() to insert stored quarantine_category values directly into SQL queries
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Check if the API endpoint is exposed to authenticated usersVerify that the /api/v1/add/mailbox endpoint is accessible to authenticated users and accepts the quarantine_category parameterAffected if The endpoint accepts quarantine_category from authenticated users without validation
You are affected if your mailcow version is prior to 2026-03b AND the API endpoint accepts unvalidated quarantine_category values that later flow into quarantine_notify.py using unsafe % string formatting in SQL queries.
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. If immediate upgrading is not feasible, implement input validation on the API endpoint and refactor quarantine_notify.py to use parameterized queries instead of % string formatting.
2026-03b
- Upgrade mailcow: dockerized to version 2026-03b or later to resolve the second-order SQL injection vulnerability in the quarantine_category field
Generated from the published advisory — verify against the referenced sources before acting.
- Consultation2.0 h
- Implementation3.0 h
- Testing3.0 h
- Review / QA1.0 h
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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-2026-40871 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
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- Version or environment caveats, and links to real fixes
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