CVE-2006-5176 in Mailenable Enterprise
Summary
by MITRE
Buffer overflow in NTLM authentication in MailEnable Professional 2.0 and Enterprise 2.0 allows remote attackers to execute arbitrary code via "the signature field of NTLM Type 1 messages".
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Analysis
by VulDB Data Team • 04/23/2026
The vulnerability identified as CVE-2006-5176 represents a critical buffer overflow flaw within the NTLM authentication implementation of MailEnable Professional 2.0 and Enterprise 2.0 email server software. This issue specifically targets the signature field within NTLM Type 1 messages, which are part of the authentication handshake process used by Microsoft's NT LAN Manager authentication protocol. The flaw arises from insufficient input validation and boundary checking when processing these authentication messages, creating an exploitable condition that can be leveraged by remote attackers to gain unauthorized system access.
The technical nature of this vulnerability stems from improper memory management within the MailEnable authentication module where the signature field of NTLM Type 1 messages is processed without adequate bounds checking. When an attacker crafts a malicious NTLM Type 1 message with an oversized signature field, the application fails to properly validate the input length before copying it into a fixed-size buffer. This classic buffer overflow condition allows the attacker to overwrite adjacent memory locations, potentially corrupting the program's execution flow and enabling arbitrary code execution with the privileges of the affected service account. The vulnerability operates at the application layer and can be exploited over network connections without requiring authentication, making it particularly dangerous for email server environments.
The operational impact of this vulnerability extends beyond simple code execution, as it provides attackers with a potential foothold for further compromise within the network infrastructure. Email servers often serve as critical components in enterprise environments, and successful exploitation could lead to unauthorized access to sensitive email communications, potential data exfiltration, and use of the compromised server as a pivot point for attacking other internal systems. The vulnerability affects both MailEnable Professional and Enterprise editions, indicating it was present in multiple product variants and likely impacted a significant portion of email server deployments using this software. The fact that the attack vector requires only network connectivity without prior authentication makes this particularly concerning for organizations with exposed email server services.
Mitigation strategies for CVE-2006-5176 should focus on immediate patch application from MailEnable vendor, as this vulnerability was addressed through official security updates. Organizations should also implement network segmentation to limit access to email services, disable unnecessary authentication protocols, and monitor network traffic for suspicious NTLM authentication patterns. The vulnerability aligns with CWE-121, which describes stack-based buffer overflow conditions, and represents a typical example of how authentication protocol implementations can introduce security weaknesses. From an ATT&CK framework perspective, this vulnerability maps to initial access and execution tactics, potentially enabling lateral movement through the compromised email server. Additionally, implementing proper input validation and boundary checking mechanisms in authentication implementations would prevent similar issues in future deployments, emphasizing the importance of secure coding practices in authentication protocol development.