CVE-2014-0118 in MacOS X
Summary
by MITRE
The deflate_in_filter function in mod_deflate.c in the mod_deflate module in the Apache HTTP Server before 2.4.10, when request body decompression is enabled, allows remote attackers to cause a denial of service (resource consumption) via crafted request data that decompresses to a much larger size.
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Analysis
by VulDB Data Team • 09/22/2022
The vulnerability identified as CVE-2014-0118 resides within the mod_deflate module of the Apache HTTP Server, specifically in the deflate_in_filter function located in mod_deflate.c. This flaw manifests when the server is configured to decompress request bodies, creating a scenario where malicious actors can exploit the decompression process to consume excessive system resources. The vulnerability falls under the category of resource consumption attacks, which are classified as CWE-400 in the Common Weakness Enumeration catalog, representing uncontrolled resource consumption that can lead to denial of service conditions.
The technical mechanism behind this vulnerability involves the manipulation of compressed data streams that the server attempts to decompress. When a client sends a request containing compressed data that is configured to be decompressed by mod_deflate, an attacker can craft data that appears legitimate but decompresses to an exponentially larger size than the original compressed payload. This creates a scenario where the server's memory and processing resources are consumed at an unsustainable rate, leading to performance degradation or complete service unavailability. The exploit leverages the inherent characteristics of compression algorithms where small input data can produce massive output, particularly when the compression format contains repeated patterns or is malformed in specific ways.
The operational impact of this vulnerability extends beyond simple service disruption, as it can be exploited by attackers to perform sustained resource exhaustion attacks against Apache servers. This vulnerability affects Apache HTTP Server versions prior to 2.4.10, making it particularly concerning for organizations running older server configurations. The attack vector requires no authentication and can be executed through standard HTTP requests, making it accessible to any attacker with network access to the vulnerable server. The vulnerability aligns with ATT&CK technique T1499.001, which covers network denial of service, and represents a classic example of how compression algorithms can be weaponized when not properly validated or limited in resource consumption.
Organizations can mitigate this vulnerability by upgrading to Apache HTTP Server version 2.4.10 or later, which includes patches addressing the resource consumption issue in the deflate_in_filter function. Additional mitigations include implementing request size limits, configuring appropriate compression level restrictions, and monitoring for unusual patterns in request processing that might indicate exploitation attempts. Security teams should also consider implementing rate limiting and connection throttling mechanisms to prevent single clients from exhausting server resources. The fix implemented in version 2.4.10 involves stricter validation of decompressed data sizes and implementation of resource limits to prevent excessive memory allocation during decompression operations, aligning with security best practices for preventing resource exhaustion attacks.