Anatomy of a user namespaces vulnerability

An exploit posted on March 13 revealed a rather easily exploitable security vulnerability (CVE 2013-1858) in the implementation of user namespaces. That exploit enables an unprivileged user to escalate to full root privileges. Although a fix was quickly provided, it is nevertheless instructive to look in some detail at the vulnerability, both to better understand the nature of this kind of exploit and also to briefly consider how this vulnerability came to appear inside the user namespaces implementation.

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