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CVE-2026-40878— mailcow-dockerized Login Page has Reflected Parameter Injection / Wrong-Context XSS Escaping

Quick assessment

Affected
mailcow mailcow-dockerized
Exploitation
Public or AI PoC available; prioritize validation
Recommended action
Check the vendor advisory and references for a fixed version. If immediate upgrade is impossible, restrict exposure and increase monitoring.

mailcow: dockerized是mailcow开源的一个docker化的mailcow应用软件。 mailcow: dockerized 2026-03b之前版本存在跨站脚本漏洞，该漏洞源于Web界面将原始$_SERVER[ REQUEST_URI ]传递给Twig作为全局模板变量，并在JavaScript字符串字面量中渲染，且query_string助手合并所有当前$_GET参数到语言切换链接，可能导致跨站脚本攻击。

AI Predicted 6.1 Difficulty: Easy EPSS 0.98% · P61

Public Exploits 1

Nuclei · 1 CVE-2026-40878.yaml [template]

Possible ATT&CK Techniques 1 AI

T1189 · Drive-by Compromise
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I. Basic Information for CVE-2026-40878

Vulnerability Information
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Vulnerability Title
mailcow-dockerized Login Page has Reflected Parameter Injection / Wrong-Context XSS Escaping
Source: CVE Program / CVE List V5
Vulnerability Description
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.
Source: CVE Program / CVE List V5
CVSS Information
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
Source: CVE Program / CVE List V5
Vulnerability Type
在Web页面生成时对输入的转义处理不恰当(跨站脚本)
Source: CVE Program / CVE List V5
Vulnerability Title
mailcow: dockerized 跨站脚本漏洞
Source: CNNVD (China National Vulnerability Database)
Vulnerability Description
mailcow: dockerized是mailcow开源的一个docker化的mailcow应用软件。 mailcow: dockerized 2026-03b之前版本存在跨站脚本漏洞，该漏洞源于Web界面将原始$_SERVER[ REQUEST_URI ]传递给Twig作为全局模板变量，并在JavaScript字符串字面量中渲染，且query_string助手合并所有当前$_GET参数到语言切换链接，可能导致跨站脚本攻击。
Source: CNNVD (China National Vulnerability Database)
CVSS Information
N/A
Source: CNNVD (China National Vulnerability Database)
Vulnerability Type
N/A
Source: CNNVD (China National Vulnerability Database)

Affected Products

Vendor Product Affected Versions CPE Subscribe
mailcow mailcow-dockerized < 2026-03b -

II. Public POCs for CVE-2026-40878

# POC Description Source Link Shenlong Link
1 mailcow < 2026-03b reflects raw REQUEST_URI into JavaScript and href links on the login page, allowing attackers to inject parameters that break JS logic and enable phishing. https://github.com/projectdiscovery/nuclei-templates/blob/main/http/cves/2026/CVE-2026-40878.yaml POC Details
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III. Intelligence Information for CVE-2026-40878

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Vendor Advisories for CVE-2026-40878 (1)

Same Patch Batch · mailcow · 2026-04-21 · 6 CVEs total

CVE-2026-40871 7.2 HIGH mailcow: dockerized vulnerable to Second Order SQL Injection in quarantine category via AP
CVE-2026-40875 mailcow: dockerized vulnerable to stored XSS in user login history real_rip
CVE-2026-40872 mailcow: dockerized vulnerable to stored XSS in autodiscover logs email address field
CVE-2026-40874 mailcow: dockerized missing authorization on Forwarding Hosts delete action
CVE-2026-40873 mailcow: dockerized vulnerable to stored XSS in Quarantine attachment filenames

IV. Related Vulnerabilities

Same product: mailcow-dockerized
Same vendor: mailcow
Same weakness: CWE-79

V. Comments for CVE-2026-40878

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