CVE-2000-1131 in GBook.cgi
Summary
by MITRE
Bill Kendrick web site guestbook (GBook) allows remote attackers to execute arbitrary commands via shell metacharacters in the _MAILTO form variable.
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Analysis
by VulDB Data Team • 10/11/2025
The vulnerability described in CVE-2000-1131 affects the Bill Kendrick web site guestbook application known as GBook which was widely used in the late 1990s and early 2000s for managing user comments on websites. This particular flaw represents a classic command injection vulnerability that arises from inadequate input validation within the application's form processing mechanism. The vulnerability specifically manifests in the _MAILTO form variable which is used to specify email addresses for notification purposes when new guestbook entries are submitted. When users submit data through the guestbook form, the application processes the _MAILTO parameter without proper sanitization, allowing malicious actors to inject shell metacharacters that get executed by the underlying operating system.
This vulnerability falls under the Common Weakness Enumeration category CWE-77 which specifically addresses Command Injection flaws where user-supplied data is directly incorporated into shell commands without proper validation or escaping. The attack vector operates through the web interface where remote attackers can manipulate the _MAILTO form field to include shell commands that will be executed on the server. The vulnerability is particularly dangerous because it allows for arbitrary code execution on the target system, potentially enabling attackers to gain full control over the web server, access sensitive data, or use the compromised system as a launch point for further attacks within the network infrastructure. The flaw essentially bypasses normal application security controls by leveraging the legitimate functionality of the guestbook application to execute unauthorized system commands.
The operational impact of this vulnerability extends beyond simple code execution to encompass significant security implications for web server environments. Attackers could potentially use this vulnerability to install backdoors, steal sensitive information stored in the web server, or perform denial of service attacks by executing resource-intensive commands. The vulnerability also demonstrates the critical importance of input validation in web applications, as the flaw exists purely due to the application's failure to sanitize user input before incorporating it into system commands. From a threat modeling perspective, this vulnerability aligns with ATT&CK technique T1059.001 for Command and Scripting Interpreter and T1078.004 for Valid Accounts, as it allows for privilege escalation and persistence within compromised systems. The vulnerability affects systems running vulnerable versions of the GBook application and typically requires no special privileges to exploit, making it particularly attractive to attackers seeking to compromise web servers with minimal effort.
Mitigation strategies for this vulnerability involve immediate patching of the affected GBook application to ensure proper input sanitization and validation of the _MAILTO parameter. Organizations should implement proper input filtering mechanisms that escape or remove shell metacharacters from user-supplied data before processing. Additionally, implementing web application firewalls and input validation rules can provide additional layers of protection against similar command injection attacks. The vulnerability also highlights the necessity of regular security audits and code reviews to identify and remediate similar flaws in web applications. System administrators should consider implementing principle of least privilege for web server accounts and monitor for unusual command execution patterns that might indicate exploitation attempts. Given the age of this vulnerability, the primary recommendation remains the complete removal or replacement of the affected GBook application with a modern, secure alternative that properly implements input validation and follows established secure coding practices.