CVE-2001-0400 in nph-maillist
Summary
by MITRE
nph-maillist.pl allows remote attackers to execute arbitrary commands via shell metacharacters ("`") in the email address.
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Analysis
by VulDB Data Team • 10/06/2025
The vulnerability identified as CVE-2001-0400 resides within the nph-maillist.pl script, a common component in early web-based mailing list management systems. This script serves as a gateway for users to subscribe, unsubscribe, and manage their email addresses within a mailing list environment. The flaw emerges from improper input validation and sanitization mechanisms within the script's handling of email addresses submitted by users. When an attacker crafts a malicious email address containing shell metacharacters, particularly the backtick character, the script fails to properly escape or filter these special characters before processing them within a shell context. This design oversight creates a critical security gap that allows remote attackers to inject and execute arbitrary commands on the server hosting the mailing list system. The vulnerability operates at the intersection of command injection and insecure input handling, representing a classic example of how insufficient sanitization of user-provided data can lead to complete system compromise.
The technical exploitation of this vulnerability follows a specific pattern that leverages the inherent trust placed in user inputs within the script's execution flow. When a user submits an email address containing backtick characters, these characters are interpreted by the shell as command substitution operators, effectively allowing an attacker to execute arbitrary system commands with the privileges of the web server process. The backtick character serves as a shell metacharacter that instructs the system to execute the command enclosed within the backticks and substitute the command's output in place of the original construct. This mechanism, when combined with the script's lack of proper input filtering, enables attackers to perform operations ranging from simple file enumeration to complete system takeover. The vulnerability specifically aligns with CWE-78, which identifies improper neutralization of special elements used in OS commands, and represents a fundamental flaw in the script's architecture that fails to implement proper command escaping or input validation.
The operational impact of this vulnerability extends far beyond simple data compromise, as it provides attackers with direct system-level access that can be leveraged for extensive malicious activities. An attacker who successfully exploits this vulnerability can execute commands with the privileges of the web server process, which typically runs with elevated permissions to handle mailing list operations. This access enables the attacker to read sensitive files, modify mailing list configurations, access other system resources, and potentially establish persistent backdoors for future access. The remote nature of the attack means that no local system access is required, making the vulnerability particularly dangerous as it can be exploited from anywhere on the internet. The implications for organizations using vulnerable mailing list systems are severe, as the compromise of a single mailing list script can lead to complete server takeover and subsequent access to all other services running on the same host. This vulnerability exemplifies the broader category of command injection attacks that are catalogued under the MITRE ATT&CK framework in the technique T1059, which covers command and scripting interpreters.
Mitigation strategies for this vulnerability must address both the immediate security flaw and implement broader defensive measures to prevent similar issues in the future. The most direct approach involves implementing proper input sanitization and escaping mechanisms within the nph-maillist.pl script, ensuring that all user-provided email addresses are properly validated and that special shell characters are either escaped or removed before any processing occurs. Organizations should also consider upgrading to more modern mailing list management systems that implement proper security measures and input validation. Additionally, the principle of least privilege should be enforced by running the web server process with minimal required permissions, limiting the potential damage from successful exploitation. Security monitoring should be enhanced to detect unusual command execution patterns that might indicate exploitation attempts. The vulnerability highlights the critical importance of proper input validation in web applications, particularly those that interact with system-level commands, and serves as a reminder that legacy systems often contain unpatched security flaws that can be easily exploited by attackers. Regular security audits and code reviews should be implemented to identify and remediate similar vulnerabilities across all web applications and scripts.