CVE-2002-0491 in Alguest
Summary
by MITRE
admin.php in AlGuest 1.0 guestbook checks for the existence of the admin cookie to authenticate the AlGuest administrator, which allows remote attackers to bypass the authentication and gain privileges by setting the admin cookie to an arbitrary value.
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Analysis
by VulDB Data Team • 09/16/2025
The vulnerability described in CVE-2002-0491 represents a critical authentication bypass flaw in AlGuest 1.0, a guestbook application that was prevalent in the early 2000s web application landscape. This vulnerability resides within the admin.php file which serves as the administrative interface for the guestbook system. The flaw stems from a fundamental design weakness in the authentication mechanism where the application relies solely on the presence of an admin cookie rather than implementing proper authentication validation. This primitive approach to access control creates a dangerous security gap that directly violates established security principles and standards such as those outlined in CWE-287, which addresses authentication bypass vulnerabilities.
The technical implementation of this vulnerability demonstrates a classic case of insecure authentication design where the system performs a simple cookie existence check without validating the cookie's authenticity or contents. An attacker can exploit this weakness by crafting a malicious request that sets the admin cookie to any arbitrary value, effectively granting themselves administrative privileges without proper authorization. This type of vulnerability falls under the category of weak session management and demonstrates poor adherence to security best practices that would be classified under MITRE ATT&CK technique T1078.004 for valid accounts and T1566 for credential access. The flaw essentially transforms what should be a robust authentication system into a trivial access point where mere cookie manipulation can bypass security controls entirely.
The operational impact of this vulnerability is severe and far-reaching for any system running AlGuest 1.0, as it allows remote attackers to completely compromise the administrative functionality of the guestbook application. Once authenticated, an attacker gains full control over the guestbook, enabling them to modify or delete entries, access sensitive user data, manipulate the application's configuration, and potentially use the compromised system as a foothold for further attacks within the network. The vulnerability's remote exploitability means that attackers do not need physical access or local network presence to leverage this flaw, making it particularly dangerous in web-facing applications. This type of authentication bypass vulnerability would typically result in complete system compromise according to security frameworks and can lead to data breaches, service disruption, and potential lateral movement within affected networks.
Mitigation strategies for this vulnerability require immediate implementation of proper authentication mechanisms that validate cookie contents and implement secure session management practices. Organizations should ensure that administrative cookies contain cryptographically secure tokens that are validated against server-side session data rather than relying on simple existence checks. The fix involves implementing proper session handling with unique, unpredictable session identifiers that are generated server-side and validated for authenticity. Security measures should include implementing strong random number generation for session tokens, proper cookie security attributes such as HttpOnly and Secure flags, and server-side session validation. Additionally, this vulnerability highlights the importance of input validation and proper access control implementation as recommended by OWASP Top Ten and NIST cybersecurity frameworks, which would prevent such weak authentication mechanisms from being deployed in production environments.