CVE-2026-40873 mailcow: dockerized vulnerable to stored XSS in Quarantine attachment filenames
Attackers can execute arbitrary JavaScript in admin browsers via crafted attachment filenames in the quarantine interface, leading to account takeover.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- A user has to click or open something
- Fix
- None listed
What is CVE-2026-40873?
CVE-2026-40873 is a high-severity cross-site scripting vulnerability in mailcow-dockerized, published on 21 Apr 2026. An attacker can exploit it over the internet without logging in, and only if a user opens a file or follows a link.
Official 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.
Which versions are affected by CVE-2026-40873?
How do I fix CVE-2026-40873?
No fix has been published for CVE-2026-40873 yet. Limit exposure of the affected software until one is available.
Escape output for the context it lands in and set a strict Content Security Policy. Upgrading the affected component is the real fix. More about Cross-site scripting.
Is CVE-2026-40873 being exploited?
It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-40873 exists.
Sources
Also known as GHSA-2xjc-rg88-jvpp.