N-able Mail Assure through April 2026 contains a design-level authorization flaw that allows an authenticated SMTP user to send outbound email using MAIL FROM addresses belonging to other tenants. When connecting to the SMTP TCP port and performing SMTP AUTH with valid credentials, the server accepts arbitrary sender domains without enforcing any domain-to-account binding. As a result, an attacker from any tenant can impersonate other tenant domains, producing messages that pass SPF and DMARC validation.
NOTE: N-able's position is that the behavior is intended functionality of its shared SMTP relay architecture and that the service does not represent that it enforces per-tenant sender-domain binding.
Attack Parameters
Attack Vector
Network
Can be exploited remotely
Attack Complexity
Low
Easy to exploit
Privileges Required
Low
Basic privileges needed
User Interaction
None
No user interaction needed
Impact Assessment
Confidentiality
None
No data leak
Integrity
Low
Partial data modification
Availability
None
No disruption
CVSS Vector v3.1
Weakness Type (CWE)
Vulnerable Products
n-able:mail assure
References 5
https://deepsec.net/speaker.html#PSLOT782
cve@mitre.org
https://gist.github.com/alessandrobertoldi/1ebe0f48aa0119d787ac0ff710057d92
cve@mitre.org
https://www.n-able.com/products/mail-assure
cve@mitre.org
http://seclists.org/fulldisclosure/2026/Jun/10
af854a3a-2127-422b-91ae-364da2661108
https://github.com/alessandrobertoldi/research/blob/main/infinity-day-at-scale-…
134c704f-9b21-4f2e-91b3-4a467353bcc0