CVE-2002-1021 in BadBlue
Summary
by MITRE
BadBlue server allows remote attackers to read restricted files, such as EXT.INI, via an HTTP request that contains a hex-encoded null byte.
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Analysis
by VulDB Data Team • 09/10/2025
The CVE-2002-1021 vulnerability affects the BadBlue web server software, which was a popular lightweight web server for windows systems during the early 2000s. This vulnerability represents a classic path traversal attack that exploits how the server processes HTTP requests containing specially crafted null byte sequences. The flaw specifically manifests when the server fails to properly sanitize input parameters, allowing attackers to bypass access controls and retrieve sensitive system files that should remain restricted. The vulnerability is particularly dangerous because it enables unauthorized access to configuration files and system resources that typically contain critical information about the server environment and user credentials.
The technical implementation of this vulnerability stems from the server's improper handling of hex-encoded null bytes in HTTP requests. When a malicious user submits an HTTP request containing a hex-encoded null byte sequence, the BadBlue server processes this input without adequate validation, causing the file access control mechanisms to be circumvented. This behavior aligns with CWE-22 Path Traversal vulnerabilities, where insufficient input validation allows attackers to access files and directories outside the intended scope. The hex-encoded null byte manipulation exploits the way certain web servers interpret and process null terminators in string operations, effectively allowing attackers to manipulate file paths and access restricted resources such as the EXT.INI configuration file that contains sensitive server information.
The operational impact of this vulnerability extends beyond simple information disclosure, as it creates a foundation for further exploitation attempts within the compromised environment. Attackers who successfully exploit this vulnerability can gain access to sensitive configuration data, potentially including database connection strings, user account information, and other system parameters that could be leveraged for additional attacks. This vulnerability directly relates to the ATT&CK technique T1083 File and Directory Discovery, as it enables attackers to enumerate and access restricted system files that would normally be protected from unauthorized access. The ability to read system configuration files significantly increases the attack surface and provides attackers with valuable intelligence for planning more sophisticated attacks against the target environment.
Organizations affected by this vulnerability should implement immediate mitigations including applying the latest security patches provided by the vendor, implementing proper input validation on all web server requests, and deploying web application firewalls to detect and block suspicious null byte sequences in HTTP traffic. Network segmentation and access control measures should be strengthened to limit the potential impact of successful exploitation attempts. The vulnerability also highlights the importance of regular security assessments and input validation testing, particularly for legacy web server software that may not receive ongoing security support. Additionally, system administrators should conduct thorough file access audits to identify any compromised systems and ensure that sensitive configuration files are properly protected against unauthorized access attempts.