CVE-2026-40873

mailcow: dockerized vulnerable to stored XSS in Quarantine attachment filenames

HIGH

8.9

CVSS Score

Published: April 21, 2026 at 07:15 PM UTC

Updated: October 26, 2026 at 09:10 PM UTC

1 product affected across 1 vendorMailcow

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Severity

HIGH8.9

Exploit prediction

EPSS 0.4%

SSVC

PoC

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

Our own answer: ranges merged, affected separated from platform-only, with confidence and review flags.

Mailcow · Mailcow

90%

v < 2026-03b

Affected range stops below 2026-3b, so it looks safe — our inference, not a vendor statement

Remediation

No guide yet

No remediation guidance has been written for this CVE yet, and no fixed version or vendor advisory is recorded against it.

References (1)

x_refsource_CONFIRM

Source: cverecord

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

SSVC — Action Prioritization

SSVCPoCNot automatableTotal impact

SSVC signals action urgency (what to patch first), separate from CVSS which measures severity.

CVSS

8.9HIGHGitHub_M

Vector?

Quick Info

StatusDEFERRED

CWE

CWE-79CWE-80

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