II. THREAT MODEL Our primary motivation for designing PRIVEXEC is to prevent the disclosure of sensitive user information involved in short-lived private execution sessions. The model for these private execution sessions is similar to the private browsing mode implemented in most modern browsers, but generalized to any user-level application. We divide the threat model we assume for this work into two scenarios, one for the duration of a targeted private execution session, and another for after a session has ended. For the first scenario, we assume that an adversary can have remote access to the target system as a normal user. Due to normal process-based isolation, the attacker cannot inspect physical memory, kernel virtual memory, or process virtual memory for processes labeled with a different user ID. Furthermore, we assume that an active network attacker candrop,reorder,ormodifytraffic,orcouldcontrolaremote endpoint, such as a web site, that the user communicates with. As with private browsing mode, we rely on common mechanisms such as SSL/TLS and user awareness to prevent the disclosure of sensitive information in this case. The threat model for the second scenario corresponds to a technically sophisticated adversary with physical access to a target system after a private execution session has ended. In this scenario, the adversary has complete access to the contents of any local storage such as hard disks or non-volatile flash memory, as well as the system RAM. It is assumed that the adversary has access to sophisticated forensics tools that can retrieve insecurely deleted data from a filesystem, or process memory pages from swap devices. Common to both scenarios is the assumption of a “benign- but-buggy”, or perhaps “benign-but-privacy-unaware”, ap- plication. In particular, our threat model does not include applications that maliciously transmit private information to remote parties, or users that do the same. However, as we describe in the next section, PRIVEXEC aims to avoid inadvertent disclosure of private information.