CVE-2000-0738 in WebShield SMTP
Summary
by MITRE
WebShield SMTP 4.5 allows remote attackers to cause a denial of service by sending e-mail with a From: address that has a . (period) at the end, which causes WebShield to continuously send itself copies of the e-mail.
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Analysis
by VulDB Data Team • 10/12/2025
The vulnerability identified as CVE-2000-0738 represents a classic denial of service flaw in email security software, specifically affecting WebShield SMTP version 4.5. This weakness stems from inadequate input validation mechanisms within the email processing pipeline, where the system fails to properly sanitize email headers before processing. The vulnerability exploits a fundamental parsing error in how the software handles the From: header field, particularly when a period character appears at the end of the email address. This seemingly minor formatting issue creates a cascading effect that fundamentally disrupts the email server's normal operations.
The technical implementation of this vulnerability resides in the email processing logic that fails to properly validate the structure of email addresses during the header parsing phase. When a malicious actor crafts an email with a From: address ending in a period, such as [email protected]., the WebShield SMTP server processes this malformed address incorrectly. The system's internal mechanisms attempt to handle this malformed address by generating duplicate copies of the email message, creating an infinite loop of self-replication. This behavior violates standard email protocol handling and demonstrates a critical flaw in input sanitization and validation procedures.
From an operational perspective, this vulnerability presents a severe threat to email service availability and system stability. The continuous generation of self-copies consumes system resources including memory, CPU cycles, and disk I/O operations, leading to progressive degradation of service performance. Network administrators may observe increasing system load, potential memory exhaustion, and ultimately complete service disruption as the system becomes overwhelmed by the recursive email processing. The vulnerability affects the core functionality of the email security appliance, potentially impacting thousands of users who rely on the protected email infrastructure.
The security implications of this vulnerability extend beyond simple resource exhaustion, as it represents a failure in basic security engineering principles and input validation. This flaw aligns with CWE-20, which describes "Improper Input Validation," and demonstrates how insufficient sanitization can create exploitable conditions. The attack vector requires minimal technical expertise and can be executed remotely, making it particularly dangerous in enterprise environments where email services are critical infrastructure components. Organizations implementing WebShield SMTP 4.5 should consider this vulnerability as part of broader security assessments and ensure proper patch management protocols are in place. The incident highlights the importance of robust input validation mechanisms and proper error handling in security appliances, particularly those handling sensitive network traffic. Mitigation strategies should include immediate patch deployment, network monitoring for unusual email processing patterns, and implementation of email header validation rules to prevent similar malformed address processing. This vulnerability also underscores the necessity of comprehensive testing procedures for security products, particularly in handling edge cases and malformed inputs that could potentially be exploited for service disruption.