CVE-2000-0833 in WinSMTP
Summary
by MITRE
Buffer overflow in WinSMTP 1.06f and 2.X allows remote attackers to cause a denial of service via a long (1) USER or (2) HELO command.
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Analysis
by VulDB Data Team • 10/12/2025
The vulnerability identified as CVE-2000-0833 represents a critical buffer overflow flaw within WinSMTP 1.06f and version 2.X email server implementations. This security weakness specifically targets the handling of USER and HELO commands in the Simple Mail Transfer Protocol (SMTP) communication process, creating an exploitable condition that can be leveraged by remote attackers to disrupt service availability. The buffer overflow occurs when the server fails to properly validate the length of input data received through these commands, allowing maliciously crafted inputs to exceed the allocated memory buffer space and overwrite adjacent memory locations.
The technical nature of this vulnerability aligns with CWE-121, which describes heap-based buffer overflow conditions where insufficient bounds checking permits memory corruption. The flaw operates at the protocol level within the SMTP server implementation, specifically targeting the command parsing mechanism that processes client requests. When an attacker sends a specially crafted USER or HELO command containing excessive data, the server's buffer management fails to properly handle the overflow, potentially leading to program termination or arbitrary code execution. This vulnerability demonstrates the classic pattern of insufficient input validation where the server does not enforce maximum length limits on user-supplied data, creating a window for memory corruption attacks.
From an operational perspective, this vulnerability presents a significant threat to email server availability and reliability. The denial of service condition can be easily exploited by remote attackers without requiring authentication or specialized privileges, making it particularly dangerous in production environments. The impact extends beyond simple service disruption to potentially compromise the entire email infrastructure, as the overflow could be leveraged to execute malicious code on the affected system. Security professionals categorize this vulnerability under the ATT&CK technique T1499.004, which covers network denial of service attacks through protocol manipulation, and represents a fundamental weakness in the server's input handling architecture.
The exploitation of this vulnerability requires minimal technical expertise and can be accomplished through standard network tools that can send malformed SMTP commands to the target server. The attack surface is broad since any system running the vulnerable WinSMTP versions is susceptible to this condition. Organizations should implement immediate mitigations including applying vendor patches, implementing input length restrictions, and configuring network firewalls to limit SMTP service access. Additionally, the vulnerability highlights the importance of proper software security practices during development phases, emphasizing the need for comprehensive input validation and bounds checking mechanisms. The issue serves as a historical example of how inadequate memory management and insufficient protocol validation can create severe security implications, particularly in network services that handle untrusted input data from remote sources.