CVE-2026-69304 in .NET
Summary
by MITRE • 09/08/2026
Improper handling of highly compressed data (data amplification) in ASP.NET Core allows an unauthorized attacker to deny service over a network.
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Analysis
by VulDB Data Team • 09/09/2026
The vulnerability described involves a critical flaw in the input validation and processing mechanisms within ASP.NET Core, specifically concerning how the framework handles HTTP requests containing highly compressed payloads. This issue stems from data amplification techniques where an attacker crafts a request with minimal uncompressed size but extremely high compression ratios or recursive compression layers. When such a payload is processed by the server's decompression logic, it expands significantly in memory before being fully validated or utilized. This discrepancy between network bandwidth consumption and server-side resource allocation creates a disproportionate strain on system resources, leading to a denial of service condition for legitimate users and potentially causing complete unavailability of the affected web application or underlying infrastructure.
From a technical perspective, this flaw represents an inefficient handling of user-supplied data where the decompression process lacks adequate safeguards against excessive expansion ratios. The server allocates memory buffers based on assumptions about payload size that do not account for worst-case compression scenarios. As the compressed stream is inflated, it consumes CPU cycles and RAM far beyond what was indicated by the initial request headers or expected content length limits. This behavior aligns with CWE-409, which describes improper handling of highly compressed data leading to memory exhaustion or resource consumption issues. The attack vector typically involves sending a specially crafted HTTP POST or PUT request with an Accept-Encoding header that triggers aggressive decompression algorithms without corresponding checks on the resulting expanded size relative to available system resources.
The operational impact of this vulnerability is severe, primarily manifesting as service degradation or total outage for applications relying on ASP.NET Core. Attackers can exploit this flaw remotely over a network by sending repeated requests with optimized compression payloads that maximize memory consumption per byte transmitted. This results in high CPU utilization due to the computational cost of decompression and potential out-of-memory errors if buffer limits are exceeded without proper exception handling or graceful degradation mechanisms. In distributed environments, such as those utilizing load balancers or reverse proxies, this vulnerability can also amplify traffic further if intermediate nodes attempt to re-compress or process the inflated data before passing it along, thereby extending the blast radius beyond a single server instance to affect entire service clusters and increasing latency for all connected clients.
Mitigation strategies must focus on implementing strict limits on decompression ratios and enforcing maximum payload sizes at multiple layers of the application stack. Developers should configure ASP.NET Core request body size limits using appropriate middleware settings such as MaxRequestBodySize, ensuring that even after decompression, the data does not exceed predefined thresholds. Additionally, custom input validation logic can be introduced to monitor compression ratios during processing and abort requests that exhibit suspicious expansion patterns. It is also advisable to disable unnecessary compression handlers or restrict them to trusted sources where possible. Regular security audits focusing on resource consumption metrics under load testing conditions will help identify similar inefficiencies before they are exploited in production environments, ensuring resilience against data amplification attacks as defined by industry standards like CWE-409 and MITRE ATT&CK techniques related to Denial of Service via application layer exploitation.