CVE-2009-1536 in NET Framework
Summary
by MITRE
ASP.NET in Microsoft .NET Framework 2.0 SP1 and SP2 and 3.5 Gold and SP1, when ASP 2.0 is used in integrated mode on IIS 7.0, does not properly manage request scheduling, which allows remote attackers to cause a denial of service (daemon outage) via a series of crafted HTTP requests, aka "Remote Unauthenticated Denial of Service in ASP.NET Vulnerability."
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Analysis
by VulDB Data Team • 04/13/2025
The vulnerability identified as CVE-2009-1536 represents a critical denial of service weakness affecting Microsoft ASP.NET implementations within the .NET Framework versions 2.0 SP1 and SP2, along with 3.5 Gold and SP1. This flaw specifically manifests when ASP.NET operates in integrated mode on Internet Information Services 7.0, creating a scenario where legitimate service availability is compromised through malicious request patterns. The vulnerability stems from improper handling of request scheduling mechanisms that govern how the web server processes incoming HTTP requests, ultimately leading to daemon outages that can severely impact system availability and service delivery. This weakness allows unauthenticated attackers to exploit the system through carefully constructed HTTP requests that trigger the underlying scheduling flaw, resulting in complete service disruption without requiring any authentication credentials or privileged access.
The technical root cause of this vulnerability lies in the flawed request scheduling implementation within the ASP.NET runtime when operating in integrated mode with IIS 7.0. When multiple crafted HTTP requests are submitted in sequence, the system's internal request handling mechanism becomes overwhelmed or enters an inconsistent state where it cannot properly process subsequent requests. This mismanagement occurs during the request processing pipeline where the ASP.NET module fails to maintain proper state management and resource allocation, leading to thread exhaustion or resource deadlock conditions. The vulnerability specifically targets the interaction between the ASP.NET runtime and IIS 7.0's integrated pipeline mode, where the module's request handling logic does not adequately account for concurrent request patterns that can trigger the scheduling failure. According to CWE classification, this represents a weakness in resource management and process scheduling that falls under CWE-400, which encompasses unspecified vulnerabilities related to resource management failures.
The operational impact of CVE-2009-1536 extends beyond simple service disruption to potentially compromise business continuity and availability of web applications hosted on affected systems. Attackers can leverage this vulnerability to cause sustained daemon outages that may require system restarts to resolve, resulting in significant downtime and potential financial losses for organizations relying on affected web services. The unauthenticated nature of the attack means that any external party can exploit this weakness without requiring valid credentials or privileged access, making it particularly dangerous in public-facing web environments. Systems affected by this vulnerability can experience complete service unavailability, with applications becoming inaccessible to legitimate users until the underlying scheduling issue is resolved, either through system restarts or patch deployment. This type of denial of service attack can be particularly devastating for mission-critical applications where continuous availability is essential for business operations.
Organizations should implement immediate mitigations including applying the relevant Microsoft security patches that address the request scheduling flaw in ASP.NET integrated mode. System administrators should also consider implementing rate limiting mechanisms and request filtering to reduce the impact of potential attacks while waiting for official patches. Monitoring for unusual request patterns and implementing intrusion detection systems can help identify exploitation attempts before they cause significant service disruption. The vulnerability aligns with ATT&CK technique T1499.004 which covers network denial of service attacks, and organizations should consider implementing defensive measures such as load balancing configurations and failover mechanisms to maintain service availability. Additionally, implementing proper network segmentation and access controls can limit the attack surface, while regular security assessments should be conducted to identify similar vulnerabilities in the web application stack. The recommended approach involves both immediate patch deployment and ongoing monitoring to prevent exploitation attempts that could lead to sustained service disruption.