Microsoft Security Response Center guidance
Release Notes
Vulnerability intelligence
CVE-2026-17545 and is rated Medium severity with a CVSS score of 6.9. It is not in the current CISA KEV record we collected. That does not prove exploitation has not occurred.
Release Notes
On Windows, PHP's filesystem and stream APIs do not reject reserved device names such as CON, PRN, AUX, NUL, COM1 to COM9, LPT1 to LPT9, CONIN$ and CONOUT$ when they appear as a component of a path. An attacker-controlled filename therefore reaches CreateFileW() and opens a device instead of the regular file the application expected, which can block or hang the request and exhaust worker processes.