Executive Summary

CVE-2019-25646 is a critical buffer overflow vulnerability in Tabs Mail Carrier version 2.5.1 and earlier. It occurs in the handling of the MAIL FROM SMTP command, where a remote attacker can send a specially crafted MAIL FROM parameter containing an oversized buffer.

This buffer overflow allows the attacker to overwrite the Extended Instruction Pointer (EIP) register, enabling arbitrary code execution. Exploitation involves connecting to the SMTP service on port 25 and delivering the malicious MAIL FROM command, which can result in the execution of a bind shell payload.

Useful 0 Not Useful 0

Impact Analysis

This vulnerability allows remote attackers to execute arbitrary code on the affected system without any privileges or user interaction.

Successful exploitation can lead to the attacker gaining a bind shell on the target machine, effectively giving them remote control over the system.

The impact includes full compromise of confidentiality, integrity, and availability of the affected system, as indicated by the high CVSS scores (9.3 and 9.8).

Useful 0 Not Useful 0

Compliance Impact

I don't know

Useful 0 Not Useful 0

Detection Guidance

This vulnerability can be detected by monitoring or testing the SMTP service on port 25 for abnormal or malicious MAIL FROM commands containing oversized buffers.

A practical detection method involves connecting to the SMTP service and sending crafted MAIL FROM commands to observe if the service behaves unexpectedly or crashes.

• Use a network tool like netcat or telnet to connect to port 25: `nc <target-ip> 25` or `telnet <target-ip> 25`.
• Manually send SMTP commands to test the vulnerability: after connection, send `EHLO test`, then send a MAIL FROM command with an oversized buffer, e.g., `MAIL FROM:<` followed by a large string of characters, then `>`.
• Observe the server response or behavior for crashes or unexpected responses indicating the buffer overflow.

Additionally, automated scripts or exploit code (such as the Python script described in Resource 2) can be used to test for this vulnerability by sending the crafted MAIL FROM payload.

Useful 0 Not Useful 0

Mitigation Strategies

Immediate mitigation steps include restricting or blocking access to the SMTP service on port 25 from untrusted networks to prevent remote exploitation.

If possible, disable or restrict the Tabs Mail Carrier 2.5.1 SMTP service until a patch or update is available.

Monitor network traffic for suspicious MAIL FROM commands with unusually large payloads.

Apply any available patches or updates from the vendor addressing this buffer overflow vulnerability.

Implement intrusion detection or prevention systems (IDS/IPS) rules to detect and block attempts to exploit this vulnerability.

Useful 0 Not Useful 0