CVE-2007-6573 in QK SMTP Server 3
Summary
by MITRE
QK SMTP Server 3 allows remote attackers to cause a denial of service (daemon crash) via a long (1) HELO, (2) MAIL FROM, or (3) RCPT TO command; or (4) a long string in the message sent after the DATA command; possibly a related issue to CVE-2006-5551.
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Analysis
by VulDB Data Team • 11/06/2017
The QK SMTP Server 3 vulnerability represents a classic buffer overflow condition that manifests through malformed SMTP command sequences, specifically targeting the server's handling of extended input strings during email transmission processes. This vulnerability exists within the server's protocol implementation where it fails to properly validate or limit the length of incoming SMTP commands, creating an exploitable condition that can be leveraged by remote attackers to disrupt service availability. The flaw affects four distinct command types within the SMTP protocol: HELO, MAIL FROM, RCPT TO, and message content following the DATA command, indicating a systemic issue in input validation rather than a single point of failure. The vulnerability's classification as a denial of service condition stems from the server's inability to gracefully handle oversized inputs, resulting in daemon crashes that terminate the mail service and prevent legitimate email processing.
The technical implementation of this vulnerability involves the server's insufficient bounds checking during SMTP command parsing, where buffer overflow conditions occur when processing input strings exceeding predetermined length limits. The attacker can exploit this by sending specially crafted SMTP commands containing excessively long strings, causing the server's memory management to fail and leading to process termination. This type of vulnerability aligns with CWE-121, which describes stack-based buffer overflow conditions, and represents a variant of the broader category of input validation flaws that compromise system stability. The related nature to CVE-2006-5551 suggests this may be part of a series of similar vulnerabilities affecting the same software family or implementation patterns, indicating potential architectural weaknesses in the server's protocol handling mechanisms.
The operational impact of this vulnerability extends beyond simple service disruption to encompass potential business continuity issues and increased administrative overhead for system maintainers. Organizations relying on QK SMTP Server 3 for email services face significant risk of service outages that could affect communication workflows and customer interactions, particularly during peak email processing periods. The remote nature of the attack means that adversaries can exploit this vulnerability without requiring physical access to the system, making it particularly dangerous in networked environments where email servers serve as critical infrastructure components. The vulnerability's exploitation requires minimal technical expertise, making it accessible to a broad range of threat actors and increasing the likelihood of successful attacks against unpatched systems.
Mitigation strategies for this vulnerability should prioritize immediate patch deployment from the software vendor, as the issue represents a fundamental protocol implementation flaw that requires code-level fixes. Network administrators should implement monitoring solutions to detect unusual SMTP traffic patterns that might indicate exploitation attempts, particularly focusing on command sequences containing unusually long strings. The principle of least privilege should be applied by restricting SMTP server access to trusted networks and implementing proper firewall rules to limit exposure. Additionally, organizations should consider implementing email filtering solutions that can identify and block malformed SMTP commands before they reach the vulnerable server, providing defense-in-depth protection against this and similar buffer overflow vulnerabilities. The ATT&CK framework categorizes this as a service stoppage technique, where adversaries leverage software flaws to disrupt critical services, making it essential for organizations to maintain current vulnerability assessments and incident response procedures to address such threats effectively.