CVE-2026-62899 in .NET
Summary
by MITRE • 08/11/2026
Inconsistent interpretation of http requests ('http request/response smuggling') in .NET allows an unauthorized attacker to bypass a security feature over a network.
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Analysis
by VulDB Data Team • 08/12/2026
Http request smuggling vulnerabilities in .NET applications arise from inconsistent handling of http protocol parsing across different components and versions of the framework. This weakness occurs when the application server and proxy devices interpret the same http request differently, creating opportunities for attackers to manipulate the request flow and bypass security controls. The vulnerability stems from how .NET processes chunked transfer encoding, content length headers, and multiple request parsing methods that may not align with standard http protocol specifications. When an attacker crafts malicious requests containing conflicting or ambiguous header values, the application may process these differently than upstream proxies or load balancers, leading to a situation where portions of the request are interpreted by different components in inconsistent ways.
The technical exploitation of this vulnerability typically involves crafting http requests with malformed headers that cause different parsing behavior between the client and server components. Attackers can manipulate how chunked encoding is handled, exploit differences in content-length versus transfer-encoding header interpretation, or create ambiguous request boundaries that confuse the http parser. This inconsistency allows malicious actors to inject additional requests into existing connections or bypass authentication mechanisms by manipulating how the application processes subsequent requests within the same connection. The vulnerability often manifests when .NET applications use different http parsing libraries or components that have varying interpretations of the same http protocol constructs, creating a mismatch between what the server expects versus what it actually receives.
The operational impact of http request smuggling in .NET environments can be severe and multifaceted. Attackers can potentially bypass authentication and authorization controls, access restricted resources, perform cross-site scripting attacks through manipulated request boundaries, or even achieve privilege escalation within applications that trust the http parsing behavior. The vulnerability can affect web application firewalls, load balancers, and reverse proxies that may not properly validate or normalize http requests before forwarding them to .NET applications. Additionally, the inconsistency in handling may allow attackers to exploit business logic flaws by manipulating request flow patterns, potentially leading to data exposure, session hijacking, or denial of service conditions. Organizations using .NET frameworks across multiple servers or cloud environments face increased risk when different components have varying interpretations of http protocol behavior.
Mitigation strategies for this vulnerability require comprehensive network and application-level controls that address both the root cause and potential exploitation vectors. Organizations should implement strict http header validation and normalization at all network boundaries, ensuring consistent interpretation of chunked encoding and content-length headers across all components in the request path. Network security teams must configure firewalls, proxies, and load balancers to sanitize and normalize http requests before they reach .NET applications, using tools that enforce standard http protocol compliance. Application developers should avoid relying on ambiguous header combinations and implement explicit validation routines for all incoming http requests. Regular security testing including http smuggling attack simulations helps identify inconsistencies in parsing behavior across different components. The mitigation approach aligns with common weakness enumeration standard CWE-444 which categorizes this as improper handling of http requests, and follows ATT&CK technique T1190 for exploitation of web application vulnerabilities through protocol manipulation. Patch management becomes critical as Microsoft releases updates to address specific .NET framework parsing inconsistencies, requiring organizations to maintain current security patches across all affected systems.