CVE-2006-0042 in Libapreq2
Summary
by MITRE
Unspecified vulnerability in (1) apreq_parse_headers and (2) apreq_parse_urlencoded functions in Apache2::Request (Libapreq2) before 2.07 allows remote attackers cause a denial of service (CPU consumption) via unknown attack vectors that result in quadratic computational complexity.
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Analysis
by VulDB Data Team • 06/17/2019
The vulnerability identified as CVE-2006-0042 affects Apache2::Request module within the Libapreq2 library, specifically targeting two critical parsing functions: apreq_parse_headers and apreq_parse_urlencoded. This issue represents a classic computational complexity attack vector that exploits the underlying implementation of request parsing routines to consume excessive CPU resources. The vulnerability exists in versions prior to 2.07 of the Libapreq2 library, making it a significant concern for web applications that rely on Apache mod_perl for request processing and parameter handling.
The technical flaw manifests through quadratic computational complexity in the affected parsing functions, where the time required to process input data grows exponentially with the size of the input. This computational inefficiency occurs when remote attackers craft malicious requests that trigger the vulnerable parsing routines, causing the system to spend disproportionate amounts of CPU cycles processing what should be relatively simple header or URL-encoded parameter parsing operations. The quadratic complexity means that as input size increases, the processing time increases at a much faster rate than the input size itself, leading to significant performance degradation and ultimately denial of service conditions.
From an operational impact perspective, this vulnerability creates a substantial risk for web servers running Apache with mod_perl and Libapreq2 modules. Attackers can exploit this weakness by sending specially crafted HTTP requests that, when processed by the vulnerable parsing functions, cause the server to consume excessive CPU resources. The denial of service effect can be severe enough to make the web application unavailable to legitimate users, potentially resulting in complete service interruption. This type of attack is particularly dangerous because it can be executed with relatively simple payloads and can be performed remotely without requiring authentication or elevated privileges.
The vulnerability aligns with CWE-775, which addresses improper handling of computational complexity, and represents a variant of the broader class of resource exhaustion attacks that fall under ATT&CK technique T1499.001 for network denial of service. Organizations should prioritize patching this vulnerability by upgrading to Libapreq2 version 2.07 or later, as this update includes fixes for the computational complexity issues in the affected parsing functions. Additionally, implementing rate limiting and input validation mechanisms can provide additional defense-in-depth measures to mitigate the impact of potential exploitation attempts. The fix typically involves optimizing the parsing algorithms to eliminate the quadratic complexity behavior and ensure that computational resources are consumed proportionally to the input size rather than exponentially.