12th USENIX Security Symposium Abstract
Pp. 231-242 of the Proceedings
Preventing Privilege Escalation
Niels Provos, CITI, University of Michigan; Markus Friedl, GeNUA mbH; Peter Honeyman, CITI, University of Michigan
Many operating system services require special privilege to execute
their tasks. A programming error in a privileged service opens the
door to system compromise in the form of unauthorized acquisition of
privileges. In the worst case, a remote attacker may obtain superuser
privileges. In this paper, we discuss the methodology and design of
privilege separation, a generic approach that lets parts of an
application run with different levels of privilege. Programming
errors occurring in the unprivileged parts can no longer be abused to
gain unauthorized privileges. Privilege separation is orthogonal to
capability systems or application confinement and enhances the security
of such systems even further.
Privilege separation is especially useful for system services that
authenticate users. These services execute privileged operations
depending on internal state not known to an application confinement
mechanism. As a concrete example, the concept of privilege separation
has been implemented in OpenSSH. However, privilege separation is
equally useful for other authenticating services. We illustrate how
separation of privileges reduces the amount of OpenSSH code that is
executed with special privilege. Privilege separation prevents known
security vulnerabilities in prior OpenSSH versions including some that
were unknown at the time of its implementation.
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