CVE-2002-1496 in Null HTTP Server
Summary
by MITRE
Heap-based buffer overflow in Null HTTP Server 0.5.0 and earlier allows remote attackers to execute arbitrary code via a negative value in the Content-Length HTTP header.
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Analysis
by VulDB Data Team • 09/05/2025
The vulnerability identified as CVE-2002-1496 represents a critical heap-based buffer overflow flaw within the Null HTTP Server version 0.5.0 and earlier releases. This vulnerability specifically targets the handling of HTTP headers, particularly the Content-Length field, which serves as a fundamental mechanism for indicating the size of message body content in HTTP communications. The flaw manifests when the server processes a maliciously crafted Content-Length header containing a negative value, creating a condition where the application attempts to allocate memory on the heap using an invalid negative size parameter.
The technical exploitation of this vulnerability occurs through improper input validation within the HTTP server's parsing logic. When the Null HTTP Server encounters a negative value in the Content-Length header, it fails to properly validate this input before attempting to allocate heap memory. This validation failure results in the application allocating a negative amount of memory or allocating memory at an invalid address, leading to heap corruption. The heap-based nature of this buffer overflow means that the memory corruption affects the server's heap management structures, potentially allowing remote attackers to overwrite critical memory locations including return addresses, function pointers, or other control data structures.
The operational impact of this vulnerability extends beyond simple denial of service scenarios, as it enables remote code execution capabilities that can be leveraged by malicious actors. An attacker who successfully exploits this vulnerability can potentially inject and execute arbitrary code on the vulnerable server system with the privileges of the web server process. This represents a severe security risk for any organization relying on the affected Null HTTP Server version, as it could lead to complete system compromise, data exfiltration, or the establishment of persistent backdoors. The vulnerability affects the core functionality of the HTTP server, making it particularly dangerous in environments where web services are critical to business operations.
Mitigation strategies for this vulnerability require immediate attention and include upgrading to a patched version of the Null HTTP Server that properly validates Content-Length header values and implements proper input sanitization. Organizations should also implement network-level protections such as firewall rules that restrict access to HTTP servers and monitor for suspicious Content-Length header values. The vulnerability aligns with CWE-121, which describes heap-based buffer overflow conditions, and demonstrates characteristics consistent with ATT&CK technique T1203, involving the exploitation of software vulnerabilities for remote code execution. Additionally, this vulnerability highlights the importance of proper input validation and memory management practices in web server implementations, as outlined in various secure coding guidelines and security frameworks that emphasize the need for robust validation of all external inputs before processing.