CVE-2005-2857 in Free SMTP Server
Summary
by MITRE
Free SMTP Server 2.2 allows remote attackers to use the server as an open mail relay (spam proxy).
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Analysis
by VulDB Data Team • 07/29/2017
The vulnerability identified as CVE-2005-2857 affects Free SMTP Server version 2.2, representing a critical security flaw that enables unauthorized remote attackers to exploit the server as an open mail relay. This configuration allows malicious actors to leverage the compromised server to forward spam emails and other unwanted mail traffic without proper authentication or authorization, effectively transforming the system into a spam proxy. The issue stems from the server's default configuration that does not properly validate incoming mail relay requests, leaving the system vulnerable to abuse by threat actors seeking to distribute spam or phishing emails through legitimate email infrastructure.
The technical root cause of this vulnerability lies in the server's insufficient access control mechanisms and lack of proper relay validation. When Free SMTP Server 2.2 operates in its default configuration, it accepts mail relay requests from any remote system without requiring authentication or implementing proper access controls. This flaw directly corresponds to CWE-285, which addresses improper authorization in security-critical functions, and aligns with ATT&CK technique T1192, which involves the use of compromised systems to relay spam or phishing emails. The vulnerability exists because the server fails to implement proper SMTP relay restrictions that would prevent unauthorized systems from using it as a mail forwarding mechanism.
The operational impact of this vulnerability is significant and far-reaching for organizations utilizing the affected software. Attackers can exploit this weakness to send massive volumes of spam emails through the compromised server, potentially leading to the server's IP address being blacklisted by major email providers and spam filtering systems. This blacklisting can severely impact legitimate email communications for the organization, as their mail servers may be blocked from sending or receiving emails. Additionally, the server becomes a vector for distributing malware, phishing campaigns, and other malicious email content, potentially resulting in reputational damage, legal liability, and compliance violations under data protection regulations such as GDPR or HIPAA.
Organizations should implement immediate mitigations to address this vulnerability by configuring proper access controls and relay restrictions on the Free SMTP Server. The most effective approach involves disabling the open relay functionality and implementing proper authentication mechanisms that require valid credentials before allowing mail relay operations. Administrators should also configure the server to only accept relay requests from trusted IP addresses or networks, and implement rate limiting to prevent abuse. Network-level protections such as firewall rules and email filtering systems should be deployed to monitor and block suspicious relay activities. This vulnerability highlights the critical importance of proper network security configuration and demonstrates how default settings in security software can create significant exposure if not properly reviewed and hardened against known attack patterns. The issue underscores the necessity of following security best practices and conducting regular security assessments to identify and remediate similar configuration flaws in email infrastructure components.