Tabs Mail Carrier 2.5.1 MAIL FROM Buffer Overflow Vulnerability

Tabs Mail Carrier 2.5.1 is susceptible to a critical buffer overflow vulnerability (CVE-2019-25646) affecting the MAIL FROM SMTP command. This flaw enables unauthenticated remote attackers to execute arbitrary code on the affected system. The vulnerability stems from insufficient bounds checking when processing the MAIL FROM parameter. By sending a specially crafted MAIL FROM command containing an oversized buffer, an attacker can overwrite the EIP register, hijack control flow, and ultimately execute a bind shell payload. This vulnerability can be exploited over the network via port 25 without requiring any prior authentication, making it easily exploitable. Successful exploitation grants the attacker complete control over the vulnerable system.

Attack Chain

1. The attacker connects to the target SMTP service on port 25.
2. The attacker sends a EHLO command to initiate communication with the SMTP server.
3. The attacker crafts a malicious MAIL FROM command with an oversized buffer.
4. The attacker sends the crafted MAIL FROM command to the SMTP server.
5. The oversized buffer overwrites the EIP register in memory.
6. The overwritten EIP register points to the attacker-controlled shellcode.
7. The shellcode executes, creating a bind shell on the target system.
8. The attacker connects to the bind shell and executes arbitrary commands.

Impact

Successful exploitation of this buffer overflow vulnerability allows remote attackers to execute arbitrary code with the privileges of the Tabs Mail Carrier process. This can lead to complete system compromise, including data theft, modification, or destruction. Given the ease of exploitation and the severity of the impact, this vulnerability poses a significant risk to organizations using the affected software. There is no information on the number of victims or sectors targeted.

Recommendation

• Deploy the Sigma rule Detecting SMTP MAIL FROM Buffer Overflow to your SIEM to identify exploitation attempts targeting this vulnerability based on oversized MAIL FROM commands.
• Monitor network connections to port 25 for unusual traffic patterns, especially related to long MAIL FROM commands, to detect potential exploitation attempts (network_connection log source).
• Consider using a Web Application Firewall (WAF) or Intrusion Detection System (IDS) to inspect and filter SMTP traffic for malicious MAIL FROM commands.
• Upgrade to a patched version of Tabs Mail Carrier that addresses this vulnerability as soon as it becomes available.