mailcow-dockerized Login Page has Reflected Parameter Injection / Wrong-Context XSS Escaping

published 2026-04-21 6 mo ago modified 2026-10-26 13 d ago also EUVD-2026-24262

cvss: 2.1; version 4.0, CNA
cisa kev: Not listed; not in CISA's catalog
epss: 0.8%; EPSS 0.8% chance of exploitation in 30 days, percentile 57%
public exploits: 0; none known, plus a Nuclei check

mailcow: dockerized is an open source groupware/email suite based on docker. In versions prior to 2026-03b, the mailcow web interface passes the raw `$_SERVER['REQUEST_URI']` to Twig as a global template variable and renders it inside a JavaScript string literal in the `setLang()` helper of `base.twig`, relying on Twig's default HTML auto-escaping instead of the context-appropriate `js` escaping strategy. In addition, the `query_string()` Twig helper merges all current `$_GET` parameters into the language-switching links on the login page, so attacker-supplied parameters are reflected and preserved across navigation. Version 2026-03b fixes the vulnerability.

Patch / fix

fixed in 1

mailcow mailcow:_dockerized 2026-03b

CISA SSVC

Exploitation: none
Automatable: no
Technical impact: partial
Assessed: 6 mo ago (2026-04-22)

Exploit prediction

0.80% chance of exploitation in the next 30 days, higher than 57% of all scored CVEs (FIRST EPSS, 2026-11-08).

Exploits and checks

Nuclei template Mailcow < 2026-03b - Href Link Injection nuclei detection template

CVSS scores

assigned by	version	score	vector
CNA	4.0	2.1	CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:A/VC:L/VI:L/VA:L/SC:N/SI:N/SA:N
CNA	4.0	2.1	CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:A/VC:L/VI:L/VA:L/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X

Affected products

mailcow mailcow-dockerized

Classification

Weakness

CWE-79 Improper Neutralization of Input During Web Page Generation

References

github.com /mailcow/mailcow-dockerized/security/advisories/GHSA-xv9r-j862-5hqf

Sources

CVE List CVE-2026-40878
NVD CVE-2026-40878

Fencer Vulns keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.

CPEs and fixed versions use Anchore's correction of NVD's data: Added CPE configurations because not yet analyzed by NVD.

Summary