CVE-2026-40873 HIGH

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

Vendor Mailcow
Product mailcow-dockerized
Weakness CWE-79 · XSS
Published April 21, 2026
Last update April 21, 2026
View on NVD All CVEs

CVSS base score

8.9/10
Attack vector Network
Attack complexity Low
Privileges required None
User interaction —
Confidentiality —
Integrity —

CVSS 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

What the vulnerability does

01Description

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.

Key dates

02Disclosure timeline

April 21, 2026 CVE published
April 21, 2026 Record updated