CVE-2004-0493 in HTTP Server
Summary
by MITRE
The ap_get_mime_headers_core function in Apache httpd 2.0.49 allows remote attackers to cause a denial of service (memory exhaustion), and possibly an integer signedness error leading to a heap-based buffer overflow on 64 bit systems, via long header lines with large numbers of space or tab characters.
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Analysis
by VulDB Data Team • 11/05/2024
The vulnerability identified as CVE-2004-0493 resides within the Apache HTTP Server version 2.0.49, specifically within the ap_get_mime_headers_core function that processes HTTP header information. This flaw represents a critical security weakness that can be exploited by remote attackers to compromise system availability and potentially execute arbitrary code. The vulnerability stems from inadequate input validation mechanisms when processing malformed HTTP headers, particularly those containing excessively long sequences of whitespace characters that can cause memory allocation issues during header parsing operations.
The technical implementation of this vulnerability involves the function's handling of header lines that contain an excessive number of space or tab characters, which creates a scenario where the memory allocation calculations become invalid due to improper signedness handling. When the function attempts to parse these malformed headers, it performs calculations that assume positive integer values for memory allocation sizes, but when confronted with extremely long header lines, these calculations can produce negative or excessively large values. This behavior creates a condition where the system allocates insufficient memory for the header processing buffer, leading to memory exhaustion that can cause the httpd process to crash or become unresponsive. On 64-bit systems, the vulnerability is exacerbated by integer signedness errors that can result in heap-based buffer overflows, allowing attackers to potentially overwrite adjacent memory locations.
The operational impact of this vulnerability extends beyond simple denial of service conditions to potentially enable more sophisticated attacks. The memory exhaustion aspect can be leveraged to perform resource exhaustion attacks against the web server, causing legitimate users to experience service disruption while the server process consumes excessive memory resources. The heap-based buffer overflow on 64-bit systems presents additional risks that could be exploited to execute arbitrary code, though the exploitation complexity is generally high due to modern memory protection mechanisms. Attackers can craft malicious HTTP requests containing header lines with thousands or millions of whitespace characters to trigger the vulnerability, making this a particularly dangerous issue for publicly accessible web servers.
Security practitioners should implement immediate mitigations including upgrading to Apache HTTP Server version 2.0.50 or later, which contains the necessary patches to address the memory handling and integer signedness issues. Additionally, implementing rate limiting and request size restrictions at the network level can help prevent exploitation attempts by limiting the amount of data that can be sent in a single request. The vulnerability aligns with CWE-122, which describes heap-based buffer overflow conditions, and represents a classic example of improper input validation that can lead to resource exhaustion and potential code execution. From an ATT&CK framework perspective, this vulnerability maps to the T1499.004 technique related to network denial of service, and potentially to T1059.007 for remote code execution if the heap overflow is successfully exploited. Organizations should also consider implementing intrusion detection systems that can identify and block requests containing suspicious header patterns that match the vulnerability characteristics.