CVE-2000-0053 in Commercial Internet System
Summary
by MITRE
Microsoft Commercial Internet System (MCIS) IMAP server allows remote attackers to cause a denial of service via a malformed IMAP request.
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Analysis
by VulDB Data Team • 04/20/2026
The vulnerability identified as CVE-2000-0053 affects Microsoft Commercial Internet System MCIS IMAP server implementations, representing a critical security flaw that enables remote attackers to execute denial of service attacks against affected systems. This vulnerability resides within the IMAP (Internet Message Access Protocol) server component of MCIS, which serves as a messaging infrastructure for email communication. The flaw manifests when the server fails to properly validate incoming IMAP requests, specifically those containing malformed data structures that exploit parsing inconsistencies in the protocol implementation. Such malformed requests can originate from any remote attacker with network access to the affected IMAP server port, typically port 143, without requiring authentication credentials or prior system compromise.
The technical nature of this vulnerability stems from inadequate input validation mechanisms within the MCIS IMAP server's request processing pipeline. When the server receives a malformed IMAP command sequence, the parsing routine fails to properly handle the unexpected data format, leading to abnormal program termination or resource exhaustion. This parsing failure can result in the server crashing or becoming unresponsive, thereby preventing legitimate users from accessing their email services through the affected IMAP server. The vulnerability is classified under CWE-129 as an insufficient input validation issue, specifically targeting protocol parsing components that lack proper boundary checks and error handling mechanisms. From an operational perspective, this flaw represents a significant risk to email service availability, as it allows attackers to disrupt critical business communications without requiring privileged access to the system.
The operational impact of CVE-2000-0053 extends beyond simple service disruption, potentially affecting business continuity and customer satisfaction for organizations relying on MCIS email infrastructure. Attackers can exploit this vulnerability through automated scanning tools or manual exploitation techniques, making it particularly dangerous in environments where email services are critical for business operations. The vulnerability's remote exploitability means that attackers can target affected systems from anywhere on the internet, without requiring physical access or insider knowledge of the network infrastructure. This characteristic aligns with ATT&CK technique T1499.004 for network denial of service attacks and represents a classic example of how protocol-level vulnerabilities can be leveraged for service disruption. Organizations may experience cascading effects from such attacks, as email outages can impact customer support systems, internal communications, and automated business processes that depend on email delivery.
Mitigation strategies for this vulnerability primarily involve applying Microsoft security patches and updates to the MCIS IMAP server software, which address the underlying parsing flaws in the affected implementation. System administrators should also implement network-level protections such as firewall rules that restrict access to IMAP ports from trusted networks only, and deploy intrusion detection systems capable of identifying malformed IMAP traffic patterns. Additionally, implementing proper input validation at network boundaries and applying rate limiting to IMAP connections can help reduce the impact of exploitation attempts. The vulnerability demonstrates the importance of robust protocol implementation and input validation in server-side applications, particularly those handling network communications where malformed data could lead to system instability or complete service disruption. Organizations should conduct regular vulnerability assessments of their email infrastructure and maintain updated security patches to prevent exploitation of similar protocol-level vulnerabilities.