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

Severity: high (CVSS 8.9 v4.0)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.3% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2026-04-21 · updated 2026-10-26
Weakness: CWE-79

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.

Affected products

mailcow-dockerized: before 2026-03b

References

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

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