CVE-2009-0751 in Web Server
Summary
by MITRE
Yaws before 1.80 allows remote attackers to cause a denial of service (memory consumption and crash) via a request with a large number of headers.
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Analysis
by VulDB Data Team • 04/27/2025
The vulnerability identified as CVE-2009-0751 affects Yaws web server versions prior to 1.80, presenting a significant denial of service risk that can be exploited by remote attackers. This flaw manifests when the server processes requests containing an excessive number of HTTP headers, leading to uncontrolled memory consumption and eventual system crashes. The vulnerability represents a classic resource exhaustion attack vector that can be leveraged to disrupt legitimate service availability.
The technical implementation of this vulnerability stems from inadequate input validation within Yaws' HTTP request parsing mechanism. When processing HTTP requests with numerous headers, the server fails to implement proper limits on header count or memory allocation per request. This allows malicious actors to craft requests containing hundreds or thousands of headers, each contributing to memory accumulation within the server process. The lack of bounds checking and memory management controls creates a condition where the server's memory consumption grows exponentially with each malicious request, ultimately exhausting available system resources.
From an operational perspective, this vulnerability poses severe implications for systems relying on Yaws as their web server infrastructure. The remote attack capability means that adversaries can exploit this flaw from anywhere on the network without requiring local access or authentication credentials. The resulting denial of service can impact entire applications or services hosted on affected servers, potentially causing cascading failures in dependent systems. Organizations may experience extended downtime, loss of service availability, and potential revenue impact depending on their operational requirements and service level agreements.
The vulnerability aligns with CWE-400, which categorizes "Uncontrolled Resource Consumption" as a fundamental weakness in software design. This classification reflects the core issue where the application fails to properly manage system resources during request processing. Additionally, the attack pattern corresponds to techniques described in the MITRE ATT&CK framework under the "Resource Exhaustion" tactic, specifically targeting the availability aspect of the CIA triad. The attack vector demonstrates how improperly validated input can be weaponized to consume system resources and compromise service availability.
Mitigation strategies should focus on immediate patching of Yaws installations to version 1.80 or later, which includes proper header count limits and memory management controls. Organizations should also implement network-level rate limiting and header count restrictions using reverse proxies or load balancers as additional defensive measures. Configuration changes to limit maximum header counts and request sizes can provide additional protection even if the primary vulnerability remains unpatched. Monitoring systems should be enhanced to detect unusual memory consumption patterns and excessive header counts in HTTP requests, enabling early detection of potential exploitation attempts.