CVE-2026-88092 in ASP.NET Core
Summary
by MITRE • 10/14/2026
Inconsistent interpretation of http requests ('http request/response smuggling') in ASP.NET Core allows an unauthorized attacker to perform tampering over a network.
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Analysis
by VulDB Data Team • 10/14/2026
The vulnerability described involves an inconsistency in how ASP.NET Core processes HTTP requests, specifically relating to the phenomenon known as HTTP Request Smuggling. This class of vulnerabilities arises when there is a discrepancy between the parsing logic used by a front-end proxy or load balancer and that of the back-end application server. In this specific instance within ASP.NET Core, the framework may interpret certain malformed or edge-case HTTP requests differently than an upstream network component. When such inconsistencies occur, it creates a window for an attacker to inject malicious payloads into subsequent legitimate requests by manipulating the boundaries between multiple HTTP messages sent over a single persistent connection.
From a technical perspective, this flaw typically stems from ambiguous handling of content-length headers versus transfer-encoding chunked formats. An attacker can craft a request that includes conflicting or malformed header fields designed to confuse the parser regarding where one request ends and another begins. If the front-end infrastructure strips or modifies these headers differently than ASP.NET Core does, the application server may interpret the remaining bytes as part of a new, unauthorized request rather than continuing the current transaction. This misalignment allows the attacker to effectively smuggle requests into the backend that were not intended by the client, bypassing standard security controls and access restrictions implemented at the network or proxy layer.
The operational impact of this vulnerability is significant because it enables an unauthorized actor to perform tampering over a network without direct authentication credentials for the target application. By successfully executing HTTP request smuggling, an attacker can impersonate other users, escalate privileges, bypass web application firewalls that inspect only the first packet in a smuggled sequence, or even redirect traffic to malicious endpoints. This undermines the integrity and confidentiality of communications between clients and servers, potentially leading to data exfiltration, session hijacking, or further exploitation of downstream systems depending on the architecture's trust boundaries.
This vulnerability aligns with CWE-440, which describes HTTP Request Smuggling as a design flaw where inconsistent interpretation leads to security bypasses. It also maps to MITRE ATT&CK technique T1592.003, specifically Gather Victim Host Information via Network Connection Capture, and potentially T1190 Exploit Public-Facing Application if used to gain initial access. Mitigation strategies primarily involve ensuring consistent parsing logic across all network components in the request path. Organizations should update ASP.NET Core to versions that address these specific edge cases in header validation. Additionally, deploying Web Application Firewalls with deep packet inspection capabilities can help detect and block malformed requests before they reach the application server. Regular security audits focusing on proxy-to-backend communication protocols are essential to identify and resolve any remaining discrepancies in request handling logic.