CVE-1999-1504 in Stalker Internet Mail Server
Summary
by MITRE
Stalker Internet Mail Server 1.6 allows a remote attacker to cause a denial of service (crash) via a long HELO command.
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Analysis
by VulDB Data Team • 06/05/2024
The vulnerability identified as CVE-1999-1504 affects the Stalker Internet Mail Server version 1.6, presenting a classic denial of service weakness that exploits improper input validation in the mail server's handling of SMTP commands. This issue specifically targets the HELO command, which is a fundamental part of the Simple Mail Transfer Protocol that establishes the identity of the sending mail server during the initial connection phase. The flaw represents a buffer overflow condition or inadequate string length validation that occurs when the server processes an excessively long HELO command from a remote attacker.
The technical implementation of this vulnerability stems from the server's failure to properly sanitize or limit the length of input received through the HELO command. When a remote attacker sends a malformed HELO command containing an abnormally long string of characters, the mail server attempts to process this input without adequate bounds checking. This lack of input validation creates an exploitable condition where the server's memory management routines become corrupted or overwhelmed, leading to a complete service crash and subsequent denial of service for legitimate users attempting to send or receive email communications. The vulnerability operates at the application layer of the network stack and requires no authentication to exploit, making it particularly dangerous in unpatched environments.
The operational impact of CVE-1999-1504 extends beyond simple service disruption, as it can effectively render an entire email infrastructure unusable for legitimate business operations. Organizations relying on the affected Stalker Internet Mail Server would experience complete email service outages until the server is manually restarted or the vulnerability is patched. The remote nature of the attack means that adversaries can exploit this weakness from anywhere on the internet without requiring physical access or network credentials, making it an attractive target for malicious actors seeking to disrupt communications. This vulnerability directly maps to CWE-121, which describes buffer overflow conditions in heap-based memory management, and aligns with ATT&CK technique T1499.004, which covers network denial of service attacks targeting email services.
Mitigation strategies for this vulnerability should prioritize immediate patching of the affected mail server software to address the input validation flaw in the HELO command processing. Network administrators should implement basic input validation measures such as limiting the maximum length of SMTP command parameters and configuring firewalls to monitor and restrict unusual command lengths. Additionally, deploying intrusion detection systems that can identify and alert on suspicious SMTP traffic patterns may help detect exploitation attempts. Organizations should also consider implementing redundant email services or backup mail servers to maintain business continuity during patch deployment windows. The remediation process should include thorough testing of patches in non-production environments before widespread deployment to ensure that the fix does not introduce additional compatibility issues with existing email infrastructure components.