CVE-2000-1203 in Domino
Summary
by MITRE
Lotus Domino SMTP server 4.63 through 5.08 allows remote attackers to cause a denial of service (CPU consumption) by forging an email message with the sender as bounce@[127.0.0.1] (localhost), which causes Domino to enter a mail loop.
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Analysis
by VulDB Data Team • 10/11/2025
The vulnerability described in CVE-2000-1203 represents a critical denial of service flaw affecting IBM Lotus Domino SMTP servers version 4.63 through 5.08. This issue stems from the server's inadequate handling of malformed email messages, specifically those originating from a forged sender address that appears to be from the localhost domain. The vulnerability exploits a fundamental weakness in the mail server's message routing logic, creating a condition where legitimate mail processing becomes impossible due to resource exhaustion. The flaw demonstrates how seemingly benign email header manipulation can be weaponized to disrupt critical business operations, particularly in environments where email services are essential for communication and data exchange. The vulnerability is categorized under CWE-400 as an uncontrolled resource consumption issue, which directly impacts system availability and can be classified as a resource exhaustion attack pattern.
The technical mechanism behind this vulnerability involves the forged sender address bounce@[127.0.0.1] which is designed to trigger specific behavior in the Domino mail server's routing algorithm. When the server receives an email message with this particular sender address, it attempts to deliver the message to the localhost domain, creating an infinite loop scenario where the system continuously processes the same message without resolution. This mail loop consumes excessive CPU cycles and system resources, effectively preventing legitimate email processing and service availability. The attack is particularly effective because it leverages the standard mail server behavior of attempting to resolve and deliver messages to local addresses, making it difficult to distinguish between legitimate and malicious traffic at the network level. The vulnerability is consistent with ATT&CK technique T1499.004 which involves resource exhaustion through manipulation of email systems, and represents a classic example of how network protocols can be exploited for denial of service attacks.
The operational impact of this vulnerability extends beyond simple service disruption to potentially catastrophic effects on business continuity and email infrastructure. Organizations relying on Lotus Domino servers for email services would experience complete email service degradation, with system administrators unable to process legitimate email traffic while the server remains trapped in the mail loop. The resource consumption pattern affects not only CPU utilization but also memory allocation and disk I/O operations as the system attempts to process the malformed messages repeatedly. Recovery from such an attack requires manual intervention, including server restarts and potential message queue cleanup, which can result in significant downtime and data loss. This vulnerability particularly affects enterprise environments where email systems are critical for business operations, making it a high-priority security concern for organizations with substantial email infrastructure dependencies. The attack vector demonstrates how remote attackers can exploit protocol implementation weaknesses without requiring authentication, making it an attractive target for malicious actors seeking to disrupt services. The vulnerability also highlights the importance of proper input validation and message routing logic in server applications, as it represents a failure in the server's ability to detect and reject malformed messages that could cause system instability. Organizations implementing email solutions should consider this vulnerability as part of their broader security posture assessment and ensure that proper network segmentation and email filtering mechanisms are in place to prevent such attacks from reaching critical infrastructure components.