CVE-2025-55315

CVE-2025-55315 is an HTTP request/response smuggling vulnerability (CWE-444) in Microsoft ASP.NET Core, in which inconsistent interpretation of HTTP requests between the application and other HTTP-processing components can desynchronize request handling. An authorized (low-privileged) network attacker triggers it by sending crafted HTTP requests, and gains the ability to bypass a security feature; the scope-changed CVSS 9.9 score (C:H/I:H/A:L) indicates the bypass can affect resources beyond the vulnerable component with high confidentiality and integrity impact. All applications built on affected ASP.NET Core versions are in scope, Visual Studio 2022 is listed as an affected product, and related news coverage flags QNAP NetBak PC Agent as an impacted downstream product. No public proof-of-concept or CISA KEV listing exists, so exploitation is not confirmed in the wild, but the 65.8% EPSS (99th percentile) signals a high predicted likelihood of exploitation within 30 days. Microsoft addressed the flaw as part of its recent Patch Tuesday release covering 175 vulnerabilities.

What to do: Apply Microsoft's latest security updates for ASP.NET Core (runtime/SDK components) and Visual Studio 2022 immediately; exact patched version numbers are listed in Microsoft's advisory. QNAP NetBak PC Agent users should install the updated build referenced in QNAP's advisory. Given the 65.8% EPSS, prioritize internet-facing ASP.NET Core applications—especially those behind reverse proxies or load balancers where smuggling bypasses front-end security controls—and monitor for a public PoC or KEV listing.