The popen API function in TSRM/tsrm_win32.c in PHP before 5.2.11 and 5.3.x before 5.3.1 when running on certain Windows operating systems allows context-dependent attackers to cause a denial of service (crash) via a crafted (1) \e\ or (2) \er\ string in the second argument (aka mode) possibly related to the _fdopen function in the Microsoft C runtime library. NOTE: this might not cross privilege boundaries except in rare cases in which the mode argument is accessible to an attacker outside of an application that uses the popen function.